File: PAGE8.LS of Disk: Disks/PDP8-Net/multos8
(Source file text)
* * *
P A G E 8
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Version 7-B
PROGRAM REFERENCE MANUAL
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Nov.16, 1994
PAGE8 and PAGE8 Manual Copyright (C),
1978 by DEWAR INFORMATION SYSTEMS COR-
PORATION. This manual may be reproduced
in whole or in part provided that all
such copies contain this copyright
notice.
This manual was generated with DISC's
Automatic cross-referencing and Indexing
Document generator program (ACID)
DEWAR INFORMATION SYSTEMS CORPORATION
1010 Executive Ct
Westmont, IL 60559
UNITED STATES OF AMERICA
Phone 708-850-4350
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 1 of 90
TABLE OF CONTENTS
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 3
1.1. MACRO FACILITY . . . . . . . . . . . . . . . . . . . . 3
1.2. AUTOMATIC PAGING . . . . . . . . . . . . . . . . . . . 3
1.3. EXPRESSION ANALYZER . . . . . . . . . . . . . . . . . 3
1.4. CONSTANTS . . . . . . . . . . . . . . . . . . . . . . 3
1.5. ASSEMBLER DIRECTIVES . . . . . . . . . . . . . . . . . 3
1.6. FIELD ADDRESSING . . . . . . . . . . . . . . . . . . . 3
1.7. ERROR DETECTION . . . . . . . . . . . . . . . . . . . 3
1.8. CROSS ASSEMBLY . . . . . . . . . . . . . . . . . . . . 3
1.9. CROSS-REFERENCE DIRECTORY . . . . . . . . . . . . . . 4
1.10. EXTERNAL SYMBOL DIRECTORY . . . . . . . . . . . . . . 4
1.11. LITERAL REFERENCE COUNTS . . . . . . . . . . . . . . . 4
1.12. LOCAL SYMBOLS . . . . . . . . . . . . . . . . . . . . 4
2. USING PAGE8 . . . . . . . . . . . . . . . . . . . . . . 4
3. PAGE8 RUN-TIME OPTIONS . . . . . . . . . . . . . . . . . 5
4. PAGE8 CHARACTER SET . . . . . . . . . . . . . . . . . . 8
5. PAGE8 EXPRESSION RULES . . . . . . . . . . . . . . . . . 8
6. PAGE8 OPERATOR PRECEDENCE HIERARCHY . . . . . . . . . . 9
7. PAGE8 SYMBOLS, CONSTANTS AND LITERALS . . . . . . . . . 10
7.1. SYMBOL . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. SEQUENCE SYMBOL . . . . . . . . . . . . . . . . . . . 10
7.3. LOCAL SYMBOL . . . . . . . . . . . . . . . . . . . . . 10
7.4. UNTYPED CONSTANT . . . . . . . . . . . . . . . . . . . 10
7.5. TYPED CONSTANT . . . . . . . . . . . . . . . . . . . . 10
7.6. SINGLE ASCII CONSTANT . . . . . . . . . . . . . . . . 11
7.7. DOUBLE ASCII CONSTANT . . . . . . . . . . . . . . . . 11
7.8. LITERALS . . . . . . . . . . . . . . . . . . . . . . . 11
8. PAGE8 SOURCE STATEMENT FORMAT . . . . . . . . . . . . . 11
9. PAGE8 ERROR, WARNING AND STATUS FLAGS . . . . . . . . . 12
10. WARNING AND STATUS FLAGS . . . . . . . . . . . . . . . . 17
11. OTHER PAGE8 ASSEMBLY ERRORS . . . . . . . . . . . . . . 19
12. GENERAL NOTES ON THE PAGE8 INSTRUCTION SET . . . . . . . 19
13. ISZ AND INC . . . . . . . . . . . . . . . . . . . . . . 21
14. OPERATE INSTRUCTIONS . . . . . . . . . . . . . . . . . . 21
15. SUBROUTINES IN PAGE8 . . . . . . . . . . . . . . . . . . 21
16. PAGE8 LIST OUTPUT FORMAT . . . . . . . . . . . . . . . . 23
17. CROSS REFERENCE DIRECTORY . . . . . . . . . . . . . . . 23
18. INDIRECT RUN-TIME REFERENCE OPERATOR . . . . . . . . . . 25
19. PAGE8 MACRO PROCESSOR . . . . . . . . . . . . . . . . . 25
19.1. DEFAULT MACRO ARGUMENTS . . . . . . . . . . . . . . . 27
19.2. MACRO BODY STATEMENTS . . . . . . . . . . . . . . . . 27
19.3. SYMBOLIC CONCATENATION . . . . . . . . . . . . . . . . 27
19.4. COMMENT FIELDS IN MACRO DEFINITIONS . . . . . . . . . 28
19.5. LABEL FIELD . . . . . . . . . . . . . . . . . . . . . 28
19.6. MACRO CALL LISTING . . . . . . . . . . . . . . . . . . 29
19.7. BACKWARDS ASSEMBLY BRANCHES IN A MACRO . . . . . . . . 29
19.8. INDIRECT, NUMERIC ARGUMENT REPLACEMENT . . . . . . . . 30
19.9. INDIRECT, SYMBOLIC REPLACEMENT . . . . . . . . . . . . 31
19.10. NESTING OF MACROS . . . . . . . . . . . . . . . . . . 31
19.11. MACRO CALLING SEQUENCES . . . . . . . . . . . . . . . 31
19.12. NULL ARGUMENTS . . . . . . . . . . . . . . . . . . . . 32
19.13. MACRO LIBRARIES . . . . . . . . . . . . . . . . . . . 32
19.14. LOCAL MACRO SYMBOLS . . . . . . . . . . . . . . . . . 33
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 2 of 90
19.15. CHARACTER STRING PROCESSING . . . . . . . . . . . . . 33
20. PAGE8 DIRECTIVES . . . . . . . . . . . . . . . . . . . . 35
20.1. AFIELD (EXPRESSION) . . . . . . . . . . . . . . . . . 35
20.2. AGO (SEQUENCE SYMBOL) . . . . . . . . . . . . . . 36
20.3. AIF (EXPRESSION),(SEQUENCE SYMBOL) . . . . . . . . 37
20.4. ALIGN . . . . . . . . . . . . . . . . . . . . . . . . 38
20.5. ANOP . . . . . . . . . . . . . . . . . . . . . . . . . 39
20.6. AREAD . . . . . . . . . . . . . . . . . . . . . . . . 40
20.7. AS (EXPRESSION),(EXPRESSION) . . . . . . . . . . 41
20.8. BYTE (EXPRESSION),(EXPRESSION) . . . . . . . . . . 42
20.9. CREF . . . . . . . . . . . . . . . . . . . . . . . . . 43
20.10. DC (EXPRESSION),(EXPRESSION),(EXPRESSION),... . . 44
20.11. DI (EXPRESSION) . . . . . . . . . . . . . . . . . 45
20.12. DSEC . . . . . . . . . . . . . . . . . . . . . . . . . 46
20.13. DSI (EXPRESSION) . . . . . . . . . . . . . . . . . 47
20.14. EJECT (EXPRESSION) . . . . . . . . . . . . . . . . . 48
20.15. END . . . . . . . . . . . . . . . . . . . . . . . . . 49
20.16. (SYMBOL) EQU (EXPRESSION) . . . . . . . . . . . . . 50
20.17. ERM . . . . . . . . . . . . . . . . . . . . . . . . . 51
20.18. ERROR: (USER-DEFINED ERROR MESSAGE) . . . . . . . . . 52
20.19. FIELD (EXPRESSION) . . . . . . . . . . . . . . . . . 53
20.20. FILE (SOURCE PROGRAM NAME) . . . . . . . . . . . . 54
20.21. FREE (EXPRESSION) . . . . . . . . . . . . . . . . . 55
20.22. GAP (EXPRESSION),(EXPRESSION),(EXPRESSION) . . . . 56
20.23. ISEC (EXPRESSION) . . . . . . . . . . . . . . . . . 57
20.24. LFIELD (EXPRESSION) . . . . . . . . . . . . . . . . . 58
20.25. LINK (OPERATION CODE) . . . . . . . . . . . . . . . 59
20.26. LIST . . . . . . . . . . . . . . . . . . . . . . . . . 60
20.27. LISTC . . . . . . . . . . . . . . . . . . . . . . . . 61
20.28. LISTM . . . . . . . . . . . . . . . . . . . . . . . . 62
20.29. LOAD . . . . . . . . . . . . . . . . . . . . . . . . . 63
20.30. MACRO . . . . . . . . . . . . . . . . . . . . . . . . 64
20.31. MEND . . . . . . . . . . . . . . . . . . . . . . . . . 65
20.32. MEXIT . . . . . . . . . . . . . . . . . . . . . . . . 66
20.33. MONR . . . . . . . . . . . . . . . . . . . . . . . . . 67
20.34. (SYMBOL) MSCAN (EXPRESSION),(DUMMY MACRO AGRUMENT) . 68
20.35. MSKIP . . . . . . . . . . . . . . . . . . . . . . . . 69
20.36. NOCREF . . . . . . . . . . . . . . . . . . . . . . . . 70
20.37. NOLIST . . . . . . . . . . . . . . . . . . . . . . . . 71
20.38. NOLISTC . . . . . . . . . . . . . . . . . . . . . . . 72
20.39. NOLISTM . . . . . . . . . . . . . . . . . . . . . . . 73
20.40. NOTE: (USER-DEFINED MESSAGE) . . . . . . . . . . . . 74
20.41. ORG (EXPRESSION) . . . . . . . . . . . . . . . . . 75
20.42. PAGE . . . . . . . . . . . . . . . . . . . . . . . . . 76
20.43. PART . . . . . . . . . . . . . . . . . . . . . . . . . 77
20.44. PUNCH (EXPRESSION) . . . . . . . . . . . . . . . . . 78
20.45. (SYMBOL) QUT (EXPRESSION),(EXPRESSION) . . . . . . . . 79
20.46. RADIX (EXPRESSION) . . . . . . . . . . . . . . . . . 80
20.47. RET . . . . . . . . . . . . . . . . . . . . . . . . . 81
20.48. ROOM (EXPRESSION) . . . . . . . . . . . . . . . . . 82
20.49. (SYMBOL) SET (EXPRESSION) . . . . . . . . . . . . . 83
20.50. (SYMBOL) SUB (EXPRESSION) . . . . . . . . . . . . . 84
20.51. TEXT . . . . . . . . . . . . . . . . . . . . . . . . . 85
20.52. TITLE (USER-DEFINED SUB-TITLE) . . . . . . . . . . . 86
20.53. UNLINK (OPERATION CODE) . . . . . . . . . . . . . . . 87
21. ALPHABETIC LISTING OF ALL DEFINED OPERATION CODES . . . 88
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 3 of 90
1. Introduction
PAGE8 is an extremely powerful two-pass macroassembler that runs under
OS/8 with the following special features:
1.1. Macro Facility
PAGE8 implements all of the features of large scale assembler posi-
tional macros, including forward and backward conditional and uncondi-
tional assembly branches, nesting, concatenation and character string
manipulation. Macro libraries can be conventiently handled with PAGE8.
1.2. Automatic Paging
PAGE8 automatically and optimally paginates the source input program
so that the object code fits into the PDP-8 memory addressing scheme.
1.3. Expression Analyzer
PAGE8 contains an expression analyzer that analyzes expressions accor-
ding to standard rules of precedence. Parentheses may be used to
change the order of evaluation. 5 arithmetic, 3 logical, 6 relational,
2 shift and several special unary operators are provided.
1.4. Constants
PAGE8 handles binary, octal, decimal and hexadecimal constants in
addition to two types of ASCII constants.
1.5. Assembler Directives
PAGE8 contains an extensive set of more than 50 assembler directives
that can be used to control all phases of the source assembly.
1.6. Field Addressing
PAGE8 treats the PDP-8 as a 32K processor and provides full assembler
support for symbolocally addressing all of the available memory.
1.7. Error Detection
PAGE8 incorporates a comprehensive error detection, warning and status
scheme that flags virtually all symtactic errors and many semantic
errors in the source program. Once detected, remedial action is taken
whenever possible to ensure that the final object code can be easily
patched.
1.8. Cross Assembly
With its extensive features, PAGE8 can actually be used (and HAS been
used) as a reasonable macro assembler for other computers.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 4 of 90
1.9. Cross-Reference Directory
PAGE8 automatically supplies a detailed croos-reference directory to
supplement the listing pass output. All errors, warnings and symbolic
references are collated. In the case of a symbolic reference, flags
are posted indicating whether the reference could change the value of
the addressed location (i.e. a destructive reference) and the type of
reference (literal, I/O, field reference etc.).
1.10. External Symbol Directory
As a run-time option, PAGE8 has the capability of generating an ex-
ternal symbol directory of all symbols, or just global symbols, that
were defined in the program. This symbol directory can then be used as
an input source file to assemble other programs that need the values
of those defined symbols.
1.11. Literal Reference Counts
When the current page literal pool is output, PAGE8 lists a count of
the number of references that used that literal. This is extremely
useful when patches are being made since the programmer can be im-
mediately alerted to a possibly unexpected use of the same literal
elsewhere on the page.
1.12. Local Symbols
PAGE8 incorporates local symbols which relieve the programmer from
having to invent symbolic labels that have no meaning in the program.
In addition, PAGE8 posts reference counts to local symbols which
specify the number of times that local symbol has been referenced.
2. Using PAGE8
The PAGE8 assembler requires an OS/8 system with a minimum of 16K of
memory on either a PDP-8/e or PDP-8/I type computer. Separate two-page
device handlers are permitted for both input and output. All of the
available memory above the first 12K of program space is used for the
master symbol table (unless an explicit memory directive has been
issued to OS/8). This allows about 700-850 symbols in each 4K memory
field under normal conditions.
When called, the PAGE8 assembler brings in the OS/8 Command Decoder to
get a file specification list for the assembly. PAGE8 will also sup-
port a direct call from OS/8 CCL if "PAGE8" is substituted for "PAL8"
in the appropriate CCL tables.
Up to three output and nine input files may be entered to the Command
Decoder. The first output file is for the binary output and is gen-
erated in a format suitable for the standard binary loader or the OS/8
ABSLDR program. The second and third output files are used for the
listing. If the second output device fills, PAGE8 automatically out-
puts and End-of-File, closes the file and switches to the third output
device.
The pass 3 list output should be on a device other than SYS:, since
SYS: is used for the temporary cross-reference file (CROSS.TM) which
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 5 of 90
is also build during pass 3. Failure to observe this precaution will
result in a totally scrambled listing and cross-reference directory.
If a carriage return is typed after the * of the Command Decoder,
PAGE8 outputs a two page help file on the master terminal. Striking
any character on the keyboard suppresses the listing of the help file.
The help file contains a list of all the error flags and their meaning
along with a list of all the run-time options in PAGE8.
At the start of each pass, PAGE8 identifies the pass on the master
terminal. If no object code is to be generated, PAGE8 proceeds dir-
ectly to pass 3. Three passes are only needed when both the object
code and assembly listing are to be generated at the same time. At the
end of the third pass, PAGE8 chains to the program HPSORT.7A which
handles the sort/merge of the cross-reference file and generates the
cross-reference directory and external symbols directory (depending on
the run-time options that were in effect).
The current assembly location counter is displayed in the MQ register
if one exists. Due to the complexity of this assembler, the rate at
which source statements are processed is somewhat slower than PAL8 on
small programs. On large programs, or programs where there is a sig-
nificant crross-reference directory, PAGE8 is considerably faster than
PAL8. Unlike CREF, PAGE8 can handle arbitrarily large programs since
an external sort (modified TREESORT4) is used for the cross-reference
directory.
The source program syntax is slightly different from that of PAL8. If
an existing PAL8 program is to be assembled under PAGE8, some minor
conversions will be needed. In almost all cases, however, such conver-
sions can be quickly handled with the TECO editor program.
Although any text editor program can be used to prepare the source
program (such as TECO or EDIT), there are several advantages in using
DISC's ICE editor (Intelligent Correction Editor). ICE command syntax
is virtually identical to EDIT, but has the advantage of being far
faster, providing automatic file backup and space warning, in addition
to keeping track of both the new and the original line numbers in a
program. Furthermore, the ICE editor can post flags on modified or
deleted statements which are then picked up by PAGE8 and posted on the
assembly listing as warnings. This way, the programmer has a cross-
reference of all modified and deleted statements from the most recent
editing pass through the source program.
3. PAGE8 Run-Time Options
The following special run-time options may be used in the command
string typed in to the OS/8 Command Decoder:
/A Abort assembly upon detecting an error in the source pro-
gram. The line in error is listed before PAGE8 returns to
the OS/8 Keyboard Monitor.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 6 of 90
/C Remove all comment fields and comment statements from the
list output.
/D Generate an external symbol directory of all symbols used
in the program. HPSORT generates an external symbol dir-
ectory file on the system device (SYS:) with the extension
of .SD. This file can then be used as an input file for
subsequent assemblies of programs which need this set of
equivalences. If there is no name for the pass 3 list
output file (viz. LPT was used as the output device), the
file is given the name: NONAME.SD.
/E List all the pass 1 errors and/or pass 1 output on the
pass 3 listing device with the same file name but the
extension of .LX. Pass 1 errors are normally listed on the
master terminal.
/F Replace the cross-reference directory with a simple symbol
table listing. This feature may be necessary in cases
where there is not sufficient room on the system device
for the temporary cross-reference file (CROSS.TM). It may
also be necessary in cases where the listing pass output
has to be placed on the system device. In the latter case,
it would be possible to run the listing and cross-refer-
ence directory separately.
/G This option is identical to /D except that only global
symbols are included in the external symbol directory. /G
is the normal option for general symbol directories.
/H Hexadecimal output. If this option is chosen, PAGE8 out-
puts all addresses and assembled code in hexadecimal in-
stead of octal on the final list output from pass 3. This
option is useful to programmers more familiar with hex-
adecimal than octal, or when PAGE8 is being used as a
cross-assembler for a hexadecimal-oriented computer.
/I Generate an index of contents. This option produces an
index of all the FILE and TITLE statements with the
file/section/line numbers. The index of contents is gen-
erated during pass 1, and the outputs appears on the pass
3 list device with the same file name but an extension of
.LX.
/J List all statements. Normally statements such as EJECT,
TITLE, FILE, LIST etc. are not listed. The /J option
forces all statements to be listed. Note that even when
statements are not listed, the line numbers are correctly
updated.
/L Suppress the entire listing except for the symbol dir-
ectory. Only NOTE: statements and statements with errors
will be listed.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 7 of 90
/M Assume that only an 80 column printer is available for the
cross-reference directory. HPSORT normally uses the entire
132 column width of a line printer for the listing.
/P Pass 1 list. This option causes the pass 1 output to be
listed on the console (or on the output device if the /E
option is also included). This is primarily an internal
diagnostic tool, but it can be useful in debugging complex
macros.
/S Suppress the listing of the symbol directory. The symbol
directory normally appears on the pass 3 list device with
the same name but the extension of .CF. The /S option does
not inhibit generation of an external symbol directory via
the /D or /G options.
/T Title suppression. This option suppresses the listing of
the PAGE8 title and subtitle lines. Page ejects will also
be suppressed.
/W Warnings as errors. This option instructs PAGE8 to treat
all warnings as errors. Any warning statements will then
be flagged as errors and listing in all passes along with
the error asterisks. Combined with the /L option, this
provides a convenient way of getting a quick listing of
all statements on which warnings have been posted.
/Y Suppress listing of un-referenced symbols in the symbol
directory. If a symbol is defined but never used, this
options inhibits the appearance of this symbol in the dir-
ectory. It is most useful when a large external synbol
directory is being assembled along with a program. In this
case there may be many definitions that are not needed by
the program and the /Y option prevednts their cluttering
up the cross-reference directory.
= Set default page eject count. Normally, an EJECT statement
without an expression is unconditional. If a default eject
count is supplied with this option, PAGE8 treats such
EJECT directives as conditional page ejects (see EJECT
directive for more details on conditional page ejects).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 8 of 90
4. PAGE8 Character Set
Numeric Characters: digits 0-9
Alphabetic Characters: letters `a' to `z' and `:'
Special Characters:
* Current location counter
*-+/ Arithmetic operators
= Defines current page literal expression
# Defines a page zero literal expression
. Delimits logical, shift and relational operators
. Identifies a sequence symbol
, Separates expressions
' Delimits a typed or ASCII constant
() Delimits a parenthetical expression
$ Identifies a global or macro symbol or absolute add-
ress reference
& Defines an indirect run-time assembly reference
% Unary symbolic operator to extract field address
" Identifies a double ASCII constant
? Unary symbolic definition operator or macro substitute
<> Delimits dummy macro arguments
! Identifies the listing line for a macro call
; Delimits start of a strippable macro comment
: As the first character of a symbol, inhibits appear-
ance in the cross-reference directory
5. PAGE8 Expression Rules
An expression consists of any number of symbols or numeric constants
separated by legal PAGE8 operators. All expressions are evaluated
accorlding to normal rules of precedence. Operators at the same pre-
cedence level that are adjacent are evaluated from left to right. The
normal order of evaluation may be altered by the use of parentheses.
Unary operators may appear before any symbols or numeric constants or
parenthetic expressions. If an expression is too complex (excessive
nesting of parenthetic expressions etc.) the E error flag is posted.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 9 of 90
6. PAGE8 Operator Precedence Hierarchy
In the table below, 1 represents the highest precedence and 8 rep-
resents the lowest precedence. All operators are listed in order of
increasing binding power.
OPERATOR TYPE PRECEDENCE OPERATION
-------- ---- ---------- ---------
.XO. Logical 8 Exclusive OR
.OR. Logical 7 Inclusive OR
.AN. & Logical 6 Logocal AND
.LS. Shift 5 Left Shift
.RS. Shift 5 Right Shift
.LT. Relational 4 Less than
.LE. Relational 4 Less than or equal
.EQ. Relational 4 Equal
.NE. Relational 4 Not equal
.GE. Relational 4 Greater than or equal
.GT. Relational 4 Greater than
+ Arithmetic 3 Binary addition
- Arithmetic 3 Binary subtraction
* Arithmetic 2 Binary multiplication
/ Arithmetic 2 Binary division
.MO. Arithmetic 2 Binary modulus
+ Arithmetic 1 Unary addition
- Arithmetic 1 Unary subtraction
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 10 of 90
7. PAGE8 Symbols, Constants and Literals
7.1. SYMBOL
A symbol consists of an alphabetic character followed by any number of
alphabetic or numeric characters.L There is no limit on the length
and all characters are significant. Only the first 11 characters,
however, will appear in the cross-reference directory.
7.2. SEQUENCE SYMBOL
A sequence symbol consists of a period followed by a symbol. Unlike
address labels, sequence symbols may be used in the label field of
almost all PAGE8 directives.
7.3. LOCAL SYMBOL
A local symbol consists of a digit from 0-9 followed by an `H' (mean-
ing `here') in the label field. In the operand field, a digit from 0-9
is followed by either an `F' (for `forwards') or a `B' (for `back-
wards') in order to reference the next or previous local symbol lthat
has the same digit. A detailed decription of local symbols and their
usage may be found in volume 1 of Knuth's `THE ART OF COMPUTER PRO-
GRAMMING'. Local symbols may also be used in the label field of the
SET, EQU and QUT directives. A local macro symbol is identical to a
normal local symbol except that it is prefixed in all cases with a
dollar sign ($).
7.4. UNTYPED CONSTANT
An untyped constant consists of a string of decimal digits whose value
lies in the range: 0-4095 (decimal). Note that untyped, decimal con-
stants are treated as signed numbers. If the value of the constant is
greater than 2047 (decimal), the Z warning will bed posted to indicate
that a sign change has occurred. The value of the constant will,
however, be correct. The RADIX directive controls the base of untyped
constants (the default value is 10). If the untyped constant begins
with a leading zero, this is tgreated as an alternate way of expres-
sing an octal constant. The sign change warning is not posted on
untyped constants when the radix is something other than decimal.
7.5. TYPED CONSTANT
A typed constant consists of a letter identifying the radix of the
constant followed by a string of digits or hexadecimal characters
(A-F) in the range 0-4095 (decimal) enclosed within single quotes.
Binary, octal, decimal and hexadecimal constants are allowed:
X'FF' Hexadecimal constant
O'73' Octal constant
B'110110' Binary constant
D'984' Decimal constant
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 11 of 90
7.6. SINGLE ASCII CONSTANT
A single ASCII constant consists of a quote followed by an character
from the PAGE8 character set. All characters in the range 240 (octal)
to 337 (octal) are allowed. Character codes are generated with the
parity bit always set to 1. Macros may be used to generate ASCII
constants with parity.
7.7. DOUBLE ASCII CONSTANT
A double ASCII constant consists of a double quote followed by any two
characters from the PAGE8 character set. The two characters are trun-
cated to 6-bit ASCII and combined to form a single 12-bit value. For
example, "QX would have the value 2130 (octal).
7.8. LITERALS
Any legal PAGE8 expression may be preceded by either an equals sign or
a number sign to indicate that the expression should be taken liter-
ally. PAGE8 evaluates the expression, inserts the value into the app-
ropriate literal pool (either on the current page if `=', or page zero
if `#') and uses the address of the literal in the operand field.
Literals are allowed with any operation codes or directives. Literals
can also be used to force explicit indirect memory references. In the
event thatg the operand is located in a different memory field, PAGE8
requires an explicit indirect memory reference to a literal in order
to avoid the posting of the K error flag (illegal cross field refer-
ence).
For example:
TAD TABLE would be illegal if TABLE is located
in a different memory field.
TADI =TABLE would be the correct method of ref-
erencing TABLE under these conditions.
8. PAGE8 Source Statement Format
The source program for input to PAGE8 should adhere to the following
specifications:
1. A comment line is identified by the presence of an
asterisk (*) or a slash (/) in column one of the state-
ment. A blank line consisting of just a CR/LF is per-
mitted.
2. If a label is present, it must begin in column one; other-
wise, column one should be blank. A comma is allowed after
the label (as in PAL8) but it is not required by PAGE8.
3. The operation code must appear no later than 20 character
positions after the last character in the label field (or
from column one, if there is no label on the statement).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 12 of 90
4. The operand field must appear no later than 10 character
positions after the last character of the operation code.
5. The comment field is separated from the operand field by
one or more blanks. No special character is required to
identify the start of the comment field. The only excep-
tion to the `one-blank' rule involves operation instruc-
tions. Operate instructions must be separated by two or
more blanks from the comment field since a single blank
after an operate instruction indicates that another oper-
ate instruction is to be micro-coded.
6. If an optional operand field is omitted, the comment field
should lie at least 10 character positions after the oper-
ation code.
7. A source statement should not contain more than 80 char-
actgers. If there are more than 80 characters, the remain-
ing characters are stripped and the X warning flag will be
posted.
8. Some of these specifications are slightly different inside
a macro definition. For example, in a macro definition,
comment fields are generally (but not necessarily) deli-
mited with a semicolon. The documentation on the macro
facility describes these differences in detail.
9. On input, all lower case characters are folded to upper
case and are therefore legal. Invalid control characters
are replaced with a square bracket (]).
9. PAGE8 Error, Warning and Status Flags
Error, warning and status flags consist of a single character that
appears between the line number and the address. A maximum of four
flags will be posted on a single line, although the total error count
will continue to be incremented and cross-references accumulated.
Error flags always increment the error count and cause two asterisks
to appear in the left margin; warning and status flags do neither. The
following error flags may be posted by the PAGE8 assembler:
A Autopaging exception error. An attempt was made to refer-
ence a symbol located on a page other than the current page
or page zero with an indirect memory reference. A paging
link is generated on the current page with a value of zero
and an indirect reference assembled to it. In PAGE8 pro-
grams, it is generally best to reserve a small set of tem-
porary cells on page zero through which explicit indirect
references may always be executed without addressing pro-
blems.
B An attempt has been made to resetr either the assembly ori-
gin or the assembly field backwards within a given ISEC
area. Due to constraints of automatic paging, PAGE8 will
not allow this to happen. A HLT instruction is assembled
instead, so that the memory address can be readily
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 13 of 90
identified. Efficient use of the two ISEC areas and the
relocation directives effectively removed this restriction.
C An illegal character was found in an expression when PAGE8
was scanning for an operand. The most likly cause of the
error is adjacent operators or an incorrect number of sub-
expressions in the operand field.
D Duplicate symbolic label. PAGE8 found a symbolic label
which had either been used previously as a label or which
had been previously defined via an EQU, QUT or SET dir-
ective.
E Expression is too complex (expression analyzer stack over-
flowed). The expression must be broken down into two (or
more) simpler expressions.
F Error in number of Fields. PAGE8 found an incorrect number
of expressions in the operand field of a statement. If too
many, the extra expressions were ignored. If too few, a
value of zero was return for each missing expression.
G Group error on microcoded operates. One (or more) of the
operate instructions microcoded does not belong to the same
group as the first operate instruction. This flag is also
posted if the operate instructions are in the same group
but have incompatible bit assignments. A halt instruction
is assembled instead. The error may also have been caused
by a failure to leave at least two blanks between the last
operate instruction and the start of the comment field.
NOTE: PAGE8 does not permit HLT to be microcoded with and
skip instructions (use DSI or a macro in the rare event
that a microcoded HLT instruction is needed).
H An illegal character was found in a typed constant. PAGE8
returns a value of zero for the constant. This error flag
is also posted if a carriage return is found immediately
after thke single or double quote of an ASCII constant.
I Illegal operand displcement. PAGE8 requires that the absol-
ute displacement from the first symbolic tag in an operand
field of a memory reference instruction be less than or
equal to 77 (octal) (paging adjustment restriction). For
example, a statement such as `JMP *-0123' is illegal while
`JMP TABLE+040' would be perfectly legal.
J PAGE8 fould that the operand field of a RET directive (ret-
urn from subroutine) contained a symbolic address which had
not been defined as a subroutine entry point via the SUB
directive.
K Memory field overflow or illegal field reference. In the
first case, PAGE8 found that the next available memory page
was located in the next memory field. PAGE8 requires use of
the FIELD directive to switch to the next memory field.
After posting the error flag, PAGE8 sets the assembly
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 14 of 90
location counter back to zero and moves to the next memory
field. Under such conditions, the generated object code and
assembly listing will be invalid (in particular, this error
condition cannot be used as an ingenious method of overcom-
ing the restriction about setting the assembly location
backwards).
In the second case, a reference was found to a location
that could not be legally referenced due to memory field
addressing problems. For example, a source statement con-
tained a direct memory reference instruction to a tagged
location in a different memory field. It should have been
coded as an indirect memory reference through a literal.
L The page zero literal pool is full. The literl in the stat-
ement on which this flag was posted has not been stored in
the literal pool on page zero. Page zero literals are built
down from location 177 (octal) to the highest location on
page zero where object code was generated. In any event,
the page zero literal pool may not go below location 20
(octal) because unexpected problems can arise if a literal
is stored in an auto-index register location.
This error flag is also posted if a literal is encountered
in a subexpression of a DC or subroutine call constant
list.
M Macro definition syntax error. This error could be cause by
a missing MEND directive, illegal use of the angle brackets
or an illegal statement within the macro definition. This
error flag will also be posted if a MEND or MEXIT directive
is encountered outside of a macro or if the maximum per-
mitted nexting level (which is 3) is exceeded during expan-
sion of the innermost macro.
N Numeric error. This error flag may be posted for any one of
the following three reasons:
(1) an attempt was made to divide by zero in an ex-
pression. In this case, a value of zero is ret-
urned for the entire expression.
(2) a non-existent radix designation was used in a
typed constant (the only legal designations are:
B, D, O and X).
(3) the value of the operand to an LDI directive is
invalid--there is no combination of microcoded
instructions that can generate the desired con-
stant.
O Undefined operation code. Apart from an obvious error, the
following possibilities should be checked:
(1) a macro definition for that operation code is
missing.
(2) a blank line had one or more blanks before the
carriage return, line feed.
(3) an UNLINK directive had been issued at some point
to remove the operation code definition from
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 15 of 90
PAGE8.
P An undefined or illegal operator was encountered in an ex-
pression. A value of zero is returned for the entire ex-
pression. A value of zero is return for the entire expres-
sion. Another common cause for a P error is a syntactically
incorrect local symbol--a single digit followed by an `F'
or a `B' identifies a local symbol. If a character other
than `F' or `B' is present, PAGE8 treats it as a single
digit decimal constant followed by an illegal operator.
Q Illegal forward reference. The operand field for this oper-
ation code must only contain symbols which have been pre-
viously defined. The value of the expression is always zero
regardless of which pass the assembler is in. Unlike most
assemblers, PAGE8 is not subject to phase errors caused by
illegal forward references. Predefinition (i.e. definition
of all symbols in a prior source statement) is required for
all of the following directives: EQU, QUT, SET, MSCAN, ORG,
FIELD, AS, GAP, FREE, AIF and ROOM. In addition, the
statement: `(Symbol) QUT %*,*' is illegal in an ISEC area
(but legal in DSEC). This latter restriction is necessary
in order to avoid obscure but hightly undesirable page-
addressing errors.
R Redefinition error. An attempt has been made to redefine a
symbol with an EQU or QUT directive. Or, an attempt was
made to redefine a symbol with SET/MSCAN that had not ori-
ginally been defined with a SET or MSCAN directive. The
value of the symbol remains unchanged.
S Error in symbolic label. This error flag may be posted
under any one of the four following conditions:
(1) the directive in the operation code field is not
permitted to have a label field.
(2) the label does not begin with an alphabetic char-
acter or does not have the correct form for a
local symbol.
(3) the label is missing in a directive that requires
a label such as SET, EQU, QUT or MSCAN.
(4) the operation code field contains a call on a
macro whose definition did not contain a label
specification.
T Truncated value. The expression in the operand field is too
large for the specified operation code. The value of the
expression is truncated to the correct size by masking.
U Undefined symbol. A source statement contains a symbol
which has never been defined in the source program. Such
symbols always have a value of zero return for them.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 16 of 90
V Table overflow. The master symbol table has exceeded the
memory capacity of the computer on which the source program
is being assembled. Assembly continues but no more symbols
can be defined. On subsequent passes, such symbols will be
treated as undefined symbols and the U error flag will be
posted. This error flag could also be posted in the ex-
tremely unlikely event that too many local symbols were
used (limits: main program: 1024 (decimal) for each digit;
macro next levels one and two: 512 (decimal) for each
digit; macro next level three: 256 (decimal) for each
digit).
Y Either there is no more room for an entry in the object gap
tables (error flag posted on GAP directive) or a syntax
error was encountered in a sequence symbol (error flag pos-
ted on an AGO or AIF directive).
Z Arithmetic overflow occurred during the evaluation of an
expression. A value of zero is returned for the expression
in such cases. Overflow can occur as the result of a multi-
plication, or during the evaluation of a constant. Overflow
and underflow can occur during shift operations. To avoid
an error flag on shifts, the operand should be masked first
to ensure that only zero bits are lost during the shift
operation.
$ Missing sequence symbol or missing MEND directive on a
macro. An END directive (or EOF on the last input file) was
encountered in a macro definition, or while the assembly
was turned off. If a missing sequence symbol was the cause,
the sequence symbol for which PAGE8 was searching is listed
immediately above the flagged line.
) The parentheses in an expression do not balance. A value of
zero is returned for the entire expression.
# Missing argument on macro call. A macro call was missing an
argument required by the macro definition, or for which the
macro definition included no provision for defaulting its
value if omitted on the macro call.
* Internal pagination phase error. An internal phase error
has occurred in paging the source program (the literal pool
and assembled code have collided on the current page in
pass 2). Pagin phase error can only occur in conjunction
with some other kind of highly fatal error such as memory
field overflow or invalid usage of the UNLINK directive or
the special `&' run-time reference operator.
< Macro syntax error. A macro definition was found with a
syntax error involving the use of the dummy argument deli-
miters. The most likely cause would be unmatched angle
brackets.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 17 of 90
% Infinite loop. More than 4095 (decimal) assembly branches
have been taken at a single nexting level in a macro expan-
sion. Under such condition, an infinite loop in a macro
definition seems to be almost certain. PAGE8 exists the
macro expansion regardless of the current nexting level.
Illegal unprotected statement. The flagged statement must be
protected with a ROOM directive in an ISEC area. Generally,
the problems lies in a sequence of statements which must be
protected in order to ensure that a bad page break will not
occur. The most common examples include:
(1) a CIF or CID instruction that is not immediately
followed with a JMP or JMS.
(2) two or more consecutive skip instructions.
(3) an unprotected call to a subroutine whose entry
point has been destructively referenced (indicat-
ing that either a parameter list follows in sub-
sequent statements or that there are multiple
exit points on the return).
In the event that a ROOM directive is not actually required
(possible in some unusual cases), the programmer can simply
insert an ANOP statement in front of the flagged statement.
This will suppress generation of the error flag.
? Absolute addressing error. In order to trap out obscure
semantic errors caused by a missing = or # on an intended
literal reference, PAGE8 insists that absolute operand add-
resses be preceded with the $ operator. For example, the
statement:
AND 077
will be flagged as an error since it is very likely that
the intended statement was:
AND =077
where the 077 is a literal. If a reference to location 0077
was actually intended, it should be coded as:
AND $077
(the $ signals PAGE8 that the 077 is a location).
10. Warning and Status Flags
W Address Warning. The instruction has been assembled cor-
rectly but may not assemble correctly in the future because
of page addressing problems. This warning would be posted
if there was an indirect memory reference through a loca-
tion on the current page. In future assemblies the page
break may occur at a different place at which time the
reference could become illegal (and the A error flag post-
ed). Judicious use of the ROOM and ALIGN directives can
prevent any problems arising in the future.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 18 of 90
X Source statement truncate warning. A line of more than 80
(decimal) caharacters has been found. All additional char-
acters after the 80th character are stripped until a carri-
age return is found. The statement is then processed norm-
ally.
+ Forwards address adjustment. This is a status flag to in-
dicate that the actual numeric valued of the operand field
has been recalculated and adjusted forwards to account for
the space taken up by the current page literal pool.
- Backwards address adjustment. This status flag indicates
that the actual numeric value of the operand field has been
recalculated and adjusted backwards to account for the
space taken up by a current page literal pool.
' Indirect paging link. This status flag indicates than an
indirect paging link has been generated by PAGE8 on a dir-
ect memory reference instruction. If the memory field
specified in the most recent AFIELD directive (or default)
differs from the current assembly field, PAGE8 will adi-
tionally post the K error flag (illegal memory field refer-
ence).
? Dubious syntax/possible semantic error. PAGE8 posts this
warning flag when it finds a statement of doubtful vali-
dity. For example, the statement:
DCA =TEMP
is syntactically correct but semantics indicate that it was
probably intended to be:
DCAI =TEMP.
This warning may also be posted when an external memory
reference has been made to a location within the current
memory field. In any event, PAGE8 assembles the instruction
according to the specified syntax of the statement.
[ Protected range. This status flag is posted on any state-
ment producing object code that PAGE8 determines is still
contiguously protected by the most recent ROOM directive.
Due to the complex internal processing of ROOM directives,
the programmer is advised to examine PAGE8's determination
of protection ranges rather than relying on any simple
empiracal rules.
0,2,3,4,5,6,7
Local symbol reference counts. The digit identifies the
number of references made to the local symbol in the label
field of the statement on which the count is posted. A
count of 7 is used to indicate 7 or more references to the
local symbol, while 0 indicates a likely error--there are
no references to this symbol. A count of 1 is considered to
be the most common case, so no count is posted in this
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 19 of 90
case. These warnings are provided in addition to the PART
directive to aid the programmer in overcoming the most com-
mon error in the use of local symbols--a missing label will
not cause a U error flag to be posted if there is another
identical label at a previous or subsequent statement that
can be referenced without crossing a PART directive.
Z Sign change. This flag is posted on untyped, decimal con-
stants whose value exceeds 2047 (decimal) but is less than
4095 (decimal) to alert the programmer that this number
will be considered a negative number in two's complement
arithmetic. This warning flag is also posted if a sign
change occurs following the multiplication of two numbers.
@ Edit/deletion change. If the source program was prepared
with DISC's ICE editor, this warning flag indicates that
the current statement during the last edit cycle (1) was
modified or (2) follows statement(s) that were deleted.
11. Other PAGE8 Assembly Errors
USER ERROR 8 AT xxxxx
This error message indicates that PAGE8 ran out of room on
the output device. Assembly is aborted.
USER ERROR 5 AT xxxxx
This error message indicates that PAGE8 could not load the
device handler. Assembly is aborted.
USER ERROR 9 AT xxxxx
An OS/8 device handler return a fatal I/O error status to
PAGE8. Assembly is aborted.
NO CREF
PAGE8 ran out of room on the system device (SYS) for the
temporary cross-reference file (CROSS.TM). A cross-refer-
ence directory cannot be supplied. Assembly continues and
PAGE8 set the /F option so that a simple directory with
reference counts will be supplied instead.
12. General Notes on the PAGE8 Instruction Set
PAGE8 recognizes most of the standard PAL8 mnemonics. One general
departure involves memory references. Separate operation code are pro-
vided for indirect memory references, so that one writes 'TADI' rather
than 'TAD I'. On CIF, CDF and CID operation codes the operand field
should contain a memory field designation in the range 0-7 (not 10 to
70 as in PAL8).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 20 of 90
External memory references are provided with TADX, DCAX, ANDX, INCX,
JMSX and JMPX in order to facilitate cross-field memory references.
PAGE8 automatically supplies the correct CDF instruction and then gen-
erates an indirect reference through the current page literal pool
(CIF is generated for JMPX and JMSX). Except for JMSX and JMPX, PAGE8
then supplies another CDF instruction back to the field specified in
the most recent AFIELD directive (or to the current field if AFIELD
has not been used). If the operand to TADX, ANDX, DCAX, or INCX
contains a second expression, PAGE8 treats that expression as the
memory field to which the first CDF is to be generated. If none is
found, PAGE8 supplies the field address of the referenced symbol, or
if none, field zero. In the case of a JMSX or JMPX instruction, PAGE8
generates the CIF instruction but does not generate any other code
other than the instruction itself.
The following examples demonstrate PAGE8 syntax on external memory
references and also show the expanded code generated:
PAGE8 Instruction Generated Code
----------------- --------------
TADX TEMP CDF %TEMP
TADI =TEMP
CDF %*
AFIELD 3
INCX $010,6 CDF 6
INCI =$010
CDF 3
JMSX SUBR,43,X'FF' CIF %SUBR
JMSI =SUBR,43,X'FF'
(Note: in the above example, PAGE8
handles the page break problem.)
With the JMS, JMSI and JMSX memory references, a parameter list is
permitted on the same line separated by commas. The parameter list and
the assembled instruction(s) are then kept together as a group and
PAGE8 ensures that a page break will not occur at that point. Note
that instructions are not permitted as parameters in the sub-expres-
sion--a statement such as 'JMS SUBR,JMP ERROR' is not valid in PAGE8.
Any addresses supplied as parameters will be taken as absolute values
and will not be adjusted by the paging routines. The point of this
latter warning is that if a program passes an error address as a
parameter, and that error address has an offset (such as ERROR+4), it
is conceivable that the absolute address could be pointing into the
literal pool (if ERROR was located at the end of a memory page).
If the restrictions above are too sever, the subroutine call and its
arguments can be handled with a macro. The macro could then handle the
page break problem and additionally allow any kind of instructions as
arguments. Note also that the parameter list on a subroutine call is
treated just like a DC constant list--in particular, literals are
barred in sub-expressions in both cases.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 21 of 90
PAGE8 does not recognize any I/O instructions other than IOT and IOS.
Unlike PAL8, PAGE8 syntax follows the actual architecture of the PDP-8
I/O instructions: the operand field contains a 6-bit device address
followed by a 3-bit device instruction field. In this way the device
address can be equated symbolically and easily changed. The device
instruction field is always constant for a particular device. For
example, the instruction 'KSF' of PAL8 would be coded in PAGE8 as:
'IOS 3,1' and the instruction 'TLS' as 'IOT 4,6'. Note that IOT is
used for non-skip I/O instructions while IOS must be used for skip I/O
instruction. This distginction is required to avoid bad page breaks.
If the programmer prefers the standard PAL8 syntax, macros may be
written to allow compatibility.
13. ISZ and INC
PAGE8 allows a distinction to be made in connection with the use of
the ISZ instruction. When an ISZ instruction is being used purely for
the purpose of incrementing a memory location, and there is no pos-
sibility (or no intended possibility!) of its skipping, it is desir-
able to inform PAGE8 of this fact. When paging the source, PAGE8
treats ISZ specially since the fact that it might skip requires that
there be room to assemble the following instruction. Otherwise, if the
ISZ were followed with the page escape, the program could skip into
the literal pool if the ISZ instruction skipped. Using INC forms PAGE8
that the instruction will not skip and it would therefore be quite
legal to follow the INC with the page escape jump instruction. Con-
sider the example below which occurs frequently at the end of a pro-
gram loop:
INC PTR Step pointer to data
ISZ CNTR Step loop counter, test for end
JMP LOOP Loop back for more to do
In this case, a page break after the 'INC PTR' would be perfectly all
right. If an 'ISZ' was used instead (preceded with a ROOM directive to
avoid unprotected multiple skip instructions) the page break might
unnecessarily occur in front of the first instruction above. Note that
the use of INC is not required--it merely allows PAGE8 to do an
optimal job of the page packing.
14. Operate Instructions
PAGE8 recognizes all the standard PDP-8 operate instructions. In addi-
tion, PAGE8 recognizes a `pseudo-instruction': LDI for `load im-
mediate'. The operand field is evaluated and PAGE8 supplies the app-
ropriate microcoded operate instruction. The following values are
allowed in the operand field (note that 64 is only possible with the
PDP-8/e BSW instruction):
1 2 3 4 6 -1 -2 -3 64 1024 2047 2048 3171 3172
15. Subroutines in PAGE8
Because of the special problems of automatic paging and the PDP-8
addressing architecture, special directives are used to facilitate
subroutine entry and exits. The SUB directive generates an indirect
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 22 of 90
jump instruction followed by the actual cell for the entry point. If
an off-page exit is needed, the RET directive will generate an in-
direct JMP through a paging link to the first JMP instruction gen-
erated by the SUB directive. If the entry point is on the same page as
the RET directive, RET generates an indirect JMP through the actual
entry point to the subroutine.
The example below should clarify the use of SUB and RET directives:
PAGE8 Instruction Generated Object Code
----------------- ---------------------
PROCESS SUB (expr) JMPI *+1
PROCESS DC (expr)
RET PROCESS JMPI PROCESS (On-page)
-----------------------------------------------------------
CALC SUB JMPI *+1
PROCESS HLT
RET CALC JMPI =CALC-1 (Off-page)
Note that SUB can take an optional expression to be generated at the
entry point. If none is supplied, PAGE8 assembles a HLT instruction
instead.
PAGE8 keeps track of whether there has been a destructive reference to
the entry point of a subroutine in order to catch unprotected calls. A
destructive reference (such as ISZ, etc.) indicates that the sub-
routine either has an argument list, or may have several different
return points. If so, and the parameters are not in line (as a con-
stant list), PAGE8 insists that the JMS(X) be protected with a ROOM
directive (although PAGE8 cannot check that the correct number of
statements is being protected).
Occasionally, however, the destructive reference may not actually in-
dicate that the subroutine call has to be protected. A very typical
case would occur with the initialization of co-routine entry points.
Advantage can be taken of the fact that PAGE8 checks for an offset in
the operand field of the destructive instruction but does not check
the value of that offset. If there is an offset to the subroutine
address, PAGE8 reasonably assumes that the reference does not involve
the actual entry point to the subroutine. This fact provides a simple
way of avoiding the check for a protected call to the sub-
routine--simply by appending +0 to the reference. For example, when
initializing the entry point to a coroutine with a DCA instruction,
the following statement could be used:
DCA PROCESS+0
PAGE8 will not consider the above statement to be a destructive refer-
ence to the PROCESS subroutine.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 23 of 90
16. PAGE8 List Output Format
The assembled list output from PAGE8 includes the FILE and TITLE text
strings at the head of each page. On a typical source statement, the
first numeric field is the three part line number. The first number is
the current input file number (0-9). The second number is the `page'
number as delimited by form feed characters generated byh the editor
program (ICE, TECO, EDIT). If no form feed characters are present in
the input sourcd program, a `page' is considered to consist of 999
lines. The third number is the line number within that page.
The second numeric field is the full 5 digit address field. If reloca-
tion is in effect, an asterisk will be lposted after this field. The
third field contains the assembled object code.
On the dump of the literal pool (current page or page zero), a fourth
numeric field appears which contains the current/zero page literal
reference count. Note that this field is in the_ current output radix
(octal or hexadecimal) and not in decimal. When patching entries in
the literal pool, this field makes it easy to avoid patching a literal
which is referenced elsewhere on the lpage possibly for a different
purpose (it might also be used as a paging link, for example).
Page zero literals are dumped whenever a FIELD or END directive is
encountered, or when the end of the last input field is reached. In an
ISEC area, the last assembled instruction on each PDP-8 page is a 5777
(octal) which provides the escape to the first location in the next
page (or next available page if the next page falls in an object gap
and the current program sections lies in ISEC 0).
Error flags and warnings are posted between the three part line number
and the address field. Up to four flags may be posted. There may be
more than four erors in a statement, but only the first four erors or
warnings cause flags to be posted.
In the case of a QUT statement, where the operand field actually
contains a 15-bit address field, the full 15- address appears in the
object field as a 5 digit octal number.
17. Cross Reference Directory
At the end of pass 3, PAGE8 chains to the HPSORT program in order to
process the cross-reference directory. A temporary file called
CROSS.TM is built during pass 3 by PAGE8. CROSS.TM contains all the
raw cross-reference information. HPSORT processes this file and sorts
it. CROSS.TM is deleted by HPSORT just before returning to the OS/8
Keyboard Monitor.
Following the program assembly statistics (total source statement
count, number of symbols, core used, etc.), the cross-reference lists
for all errors and warnings (if any) are printged. Following this is
the cross-reference directory of all symbols defined in the program.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 24 of 90
The first field after the symbol name is present only if the symbol
was defined as an address (either as a label on a statement or defined
via a QUT directive). In this case, a single digit identifies the
memory field address of the symbol. This field will be left blank for
symbols defined via SEDT, MSCAN, EQU, or MACRO.
The second field contains the 12-bit value of the symbol unless the
symbol was a macro (in which case the field is blank). The third field
contains a single letter identifying the type of symbol:
S SET or MSCAN
E EQU
M MACRO
A Address (defined as a label or via QUT)
If the /F option was used (or if PAGE8 ran out of room for the
CROSS.TM file and forced /F on), the fourth field is the reference
count for that symbol. lOtherwise, the remaining fields contain the
cross-reference directory of all references to that symbol. The first
cross reference field is always the lpoint at which the symbol was
defined. The remaining field contains all the references to that sym-
bol in order of appearance in the source program. After the three-part
file/page/line number for the reference, various flags are lposted to
further idedntify the type of reference.
In the case of cross-reference lists for errors or warnings, the
actual error or warning flag is posted after the hyphen. For symbols,
the following flags are used:
D Destructive memory reference
N Non-destructive memory reference
I IOT or operate instruction reference
A Assembler directive reference
= Literal reference (current or zero page)
% Memory field reference or definition reference
A small help file to remind the programmer of the meaning of these
flags may be obtained by issuing a direct RUN command on the HPSORT
program.
Local symbols, symbols beginning with a colon and macros that do not
begin with a period are all inhibited from appearing in the cross-
reference directory (although they are included in the total symbol
count).
In the evednt that only reference counts are being supplied, there
will be a digit from 1 to 7 where 7 indicates that there were 7 or
more references to that symbol. A count of 1 indicates that the symbol
was defined but never referenced.
This feature of automatically switching to the third output file (if
the second output file overflows) is in PAGE8, but not HPSORT. How-
ever, if PAGE8 has already moved to the third output file, HPSORT will
generate the cross-reference file on the third output device.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 25 of 90
If HPSORT.xx is not found on the system device at the start of the
assembly, the message: `NO HPSORT.xx' will appear on the console prior
to the start of pass one.
18. Indirect Run-Time Reference Operator
By preceding a symbol with the `&' unary operator, PAGE8 will return
as the value of that symbol the current contents of the memory loca-
tion addressed by the symbol. The addressed memory location has noth-
ing to do with the program being assembled. Before describing this
feature further, the following example should be examined:
DATE QUT 1,07666 `DATE' has address of OS/8 date word
CDATE EQU &DATE `CDATE' now has value of date word
Following the execution of these two statements, the symbol `CDATE'
has the actual value of the OS/8 date word since it was equated to the
contents of memory location 17666 (octal).
This feature provides extraordinary capabilities to the programmer.
For example, a macro can be written to take the binary date word and
convert it into an ASCII text string. The text string could lthen be
used in the program as a message. With this a program could not only
print out a version number but also print out the precise date on
which the progrm was last assembled.
Another very useful way of utilizing this feature is to gain access to
the OS/8 Command Decoder tables to look at the run-time switches that
were set for running PAGE8. In the example below, a program implements
a run-time switch that is not used by PAGE8 (/B) for the purpose of
stripping out some conditional code. If the /B switch is specified,
the code is not assembled; if the /B switch is not used, the code is
assembled:
SWIT0 QUT 1,07643 A-L switches in Decoder tables
AIF &SWIT0.AN.02000,.SKIP Skip if /B set
... .....
... ..... This code assembled if /B not set
... .....
.SKIP ANOP Assembly continues in any event
The second statement isolates bit 1 of the contents of location 07643
(octal) which will be set if /B was used. If set, the expression is
true and the assembly branch will be taken.
19. PAGE8 Macro Processor
This section describes all of the features of the macro processor. In
the following documentation it is assumed that the programmer is reas-
onably familiar with the concept of macros.
The MACRO directive and associated definition may only appear at cer-
tain points in a PAGE8 source program. In all cases, the macro defini-
tion must, of course, precede the first invocation of the macro. Any
macro calls made prior to the macro definition will be treated as
undefined operation codes and the O error flag will be posted. In
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 26 of 90
general, macros should appear in the following positions in the source
program:
1. Before the end of page zero in any memory field.
2. In any DSEC area.
3. In any memory page prior to generation of any links or
literals.
There are also some highly obscure, additional internal restrictions
on the third item, so that to be safe, a macro in this position should
be defined after an ALIGN directive or ORG directive to the start of a
memory page. If a macro definition appears at an illegal point in the
program, the M error flag will be posted and the MACRO directive
ignored.
The example below shows typical syntax for a PAGE8 macro:
MACRO Signal that definition follows
LOOP <ADDR><COUNT=CNT> Prototype header statement
<> ISZ <COUNT> Test loop counter
JMP <ADDR> Loop back if non-zero
MEND End of macro definition
The above macro provides a `LOOP' instruction that tests a loop coun-
ter (defaulted to `CNT' if no argument is supplied) and if it is non-
zero, jumps back to the address specified in the argument.
The first statement of a macro definition must be the MACRO directive.
Any operand field to the directive is treated as part of the comment
field. THe only type of label permitted is an assembly sequence sym-
bol. In all macro definitions, many of the errors are only posted in
pass 1, so the pass 1 error count must be examined carefully before
concluding that there are no assembly errors.
The second statement is the prototype header statement. No label of
any kind is permitted on this statement (not even sequence symbols).
The dummy macro arguments (up to as many as will fit on the line) are
all enclosed in angle brackets. The arguments must be con-
tiguous--separating blanks or commas are not allowed. Note that this
latter rule is different from the specification of arguments in the
actual call to the macro (to be described later).
The dummy macro argument names must be unique within a single defini-
tion or a D error flag will be lposted for the duplicate definition.
The dummy macro arguments are defined only within the macro defini-
tion: no confusion is caused should they happen to have the same name
as symbols that have already been defined in the program. In the
example on the previous page, it makes no difference if a symbol
already exists whose name is `ADDR'. Dummy macro argument names should
comprise standard PAGE8 symbols. Dummy arguments are encoded in a
special form within the macro tables, so that the length of the dummy
macro artument name has no affect at all on the amount of symbol table
space used to store the macro definition.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 27 of 90
The user-defined macro name must be unique. It may not duplicate any
prevcious macro name, standard PAGE8 operation code (unless previously
removed with the UNLINK directive), or user-defined symbol. For this
reason, and to avoid conflicts, user-defined macros usually (but not
necessarily) have a period as the first character of the macro name.
Also, if the macro does not begin with a period (as is the case in the
example above) the macro name will not be listed in the cross refer-
ence directory.
19.1. Default Macro Arguments
Default arguments are indicated by an equals sign following the dummy
argument name. After the equals sign, a test string can be supplied as
a default value to be substituted. If a macro call fails to supply an
argument in this position, the default argument is supplied by PAGE8
whenever that particular dummy artument appears in a body statement.
In the default text string, any characters may appear except the angle
brackets. Consider the two calls below to the macro that was defined
earlier:
Macro Call Macro Expansion
---------- ---------------
LOOP TAG,KOUNT ISZ KOUNT
JMP TAG
----------------- -------------------
LOOP TAG ISZ CNT
JMP TAG
In the second case, PAGE8 supplies a default for the missing second
argument of the text string: `CNT'.
19.2. Macro Body Statements
In the body of the macro definition, any number of statements may
appear. Dummy artuments must always appear enclosed within angle
brackets. If the angle brackets are missing, PAGE8 will not treat the
symbol as a dummy argument.
Two special characters must not appear in macro body statements: the
up-arrow (ASCII 236 (octal)) and the left-arrow or underline (ASCII
237 (octal)). These two characters are used for the internal rep-
resentation of a tab and an end-of-line.
19.3. Symbolic Concatenation
Due to the syntax of PAGE8 macro definitions, symbolic concatenation
of dummy arguments requires no special feature or operator. Consider
the example below where a symbolic reference is dependent on the macro
call to supply the last part of the full symbolic name:
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 28 of 90
Macro Call Macro Definition
---------- ----------------
ADD LABEL MACRO
ADD <ENDNAME>
----------------------- TAD MAC<ENDNAME>
Macro Expansion MEND
---------------
TAD MACLABEL
19.4. Comment Fields in Macro Definitions
Comment fields should be used freely in macro definitions to aid in
the documentation of the source program. Normally comments need not be
stored in the macro tables and for this reason, a semicolon is gener-
ally used to indicate the start of a comment field in a macro defini-
tion. When a semicolon is seen, all preceding blanks and tabs back to
the most recent character other than a blank or tab are stripped.
If the semicolon is omitted, the comment field will be stored in the
macro tables and will be seen in the macro expansion if a LISTM dir-
ective is in effect. This feature can be useful for documentation
purposes or for debugging complex macros.
Comment statements, signalled by an asterisk or slash in column 1 of
the statement, are always stripped out of macro definitions and not
stored in the macro table.
Multiple tab characters are stored as a single tab character in the
macro tables. Two or more blanks are automatically converted to a
tabl. lThis ensures that the expanded source, if listed, appears at
the normal tab lpositions on the line (PAGE8 sets tabs at every 8th
character position on a line).
19.5. Label Field
The following information describes a requirement of PAGE8 that is not
a standard feature of most macro processors. Because of the automatic
source paging and the need to generate page escapes over literal
pools, labels cannot be evaluated in PAGE8 until the object code for
the associated operation code has been generated. For this reason a
label on a macro call cannot be blindly assigned to the value of the
current location counter (as would be the case with a non-paging
assembler). In PAGE8 macros, the label is passed as a hidden parameter
to the macro and the macro definition indicates where the label is to
be placed by a left angle bracket followed immediately by a right
angle bracket in the label field of the body statement. For example,
the call to the previously defined macro `LOOP':
TAG LOOP 1B
would cause the following expansion to be generated:
TAG ISZ CNT
JMP 1B
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 29 of 90
The label field on the macro call can thus be placed on any body
statement who directive permits a label. The label on the macro call
can also appear on more than one body statement. This would be legal
if the macro used the label on SET or MSCAN directives or if the
symbol being passed was a local symbol.
If the macro definition does not include an indication of where the
label should appear, an attempt to call that macro with a label will
result in the S error flag's being posted.
The label field indication in the macro definition must appear in
column 1 of the statement. The only exception involves the special
macro call list indicator character (an exclamation point (!)) des-
cribed below.
19.6. Macro Call Listing
Normally, the macro call statement is listed as the first statement of
the macro expansion. Under some conditions, however, this could cause
the macro call to be lost. For example, if the macro begins with a
NOLIST directive, the macro call would not appear since the statement
will not be listed. To avoid this problem there is a feature to
specify on which statement the macro call is to be listed. This is
done by placing an exclamation mark (!) character as the first char-
acter on the line which contains the body statement to be used for the
listing.
The ! character is considered to precede column 1 on the statement and
does not therefore prohibit placement of any kind of label on that
statement. As a clarification of this feature, consider the following
macro which precisely describes the PAGE8 SUB directive and the manner
in which the SUB directive is listed:
MACRO
SUB <ARG=07402> ; If no argument, use HLT
ROOM 2 ; ensure contiguous room on page
JMPI *+1 ; for off-page return
!<> DC <ARG> ; generate entry point & list it
MEND
If a LISTM condition is in effect, all the source statements of the
macro expansion are listed. lThe call to the macro is then listed
before the expansion of the first line of the macro. In nexted macros,
only the call to the first macro is listed.
19.7. Backwards Assembly Branches in a Macro
Both the AIF and AGO directives are permitted in a macro. When an AGO
or AIF (with an expression that is true) is found within a macro,
PAGE8 turns the assembly off and begins the scan for the matching
sequence symbol at the START of the macro and not at the current line.
As a result, backwards assembly branches are possible allowing iter-
ative loops to be set up. Note that within a macro definition, all
sequence symbols must be unique for this feature to work properly. The
following macro will set up a table in which the length, starting
value, and incrfment value to be added to each subsequent entry are
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 30 of 90
supplied in the macro call.
MACRO
.TABLE <LENGTH><START><INDEX>
T SET <LENGTH> ; Set loop count to length
V SET <START> ; Establish starting value
.LOOP DC V ; Generate value (loop here)
V SET V+<INDEX> ; Increase value by index
T SET T-1 ; Decrement loop counter
MEND
In coding backwards assembly branches, it should be remembered that
the start of the loop should be as close as possible to the start of
the macro in order to gain speed. If there is extensive initialization
to be performed prior to the loop, it may be more efficient to use an
AGO directive to skip over the loop and do the initialization after
the loop.
19.8. Indirect, Numeric Argument Replacement
A PAGE8 symbol in a macro expansion can be replaced indirectly by a
numeric texgt string that represents the current value of that symbol.
The indirect argument replacement is signified by preceding the symbol
with a backslash () character. The numeric text string will be a 4
digit octal number (or 3 digit hexadecimal number if the /H run-time
option is in effect). This operator may not appear in front of a dummy
argument. Should this be required, the dummy argument can be used in
the operand field of a SET directive, and the label used in subsequent
statements with the backslash operator.
The following examples should clarify the use of this feature. Every
time the first macro is invoked, the symbolic argument is stored as a
constant. At the same time, a special `symbol' table is built up which
contains the addresses of each call to the macro. The second macro
would be called later on to generate a table of all the addresses that
were saved by the first macro.
MACRO
.SAVE <CON> ; Argument is some constant
CT SET CT+1 ; Index numeric part of name
TCT DC <CON> ; Generate constant and symbol
MEND
MACRO This macro generates the table
.GENTABLE
CT SET 1 ; Reinitialize numeric part
.LOOP DC TCT ; Generate address of entry
CT SET CT+1 ; Increment numeric part
AIF ?TCT,.LOOP ; Stop when no more defined
DC 0 ; Attach sentinel of zero
MEND
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 31 of 90
Note also the use of the definition operator to find out how many
symbols we actually generated. The symbols generated have names of
T0001, T0002, T0003, T0004, ...etc. The symbol that follows the `'
operator must have been defined in a prior source statement; otherwise
the Q error flag is posted for an illegal forward reference.
19.9. Indirect, Symbolic Replacement
A PAGE8 symbol in a macro expansion can be replaced indirectly by a
single letter that represents the ASCII code contained in the low
order 8 bits of the value of the symbol. This is specified by preced-
ing the symbol with an opening square bracket ([). As with the back-
slash operator, the symbol must have been previously defined and may
not be a dummy argument. This feature is generally used to reconstruct
symbolic names or tgext strings from numeric arguments.
The following example should clarify the use of this feature. This
macro takes a single argument and converts it to two characters
(treatihe argument as a packed, 6-bit representation of two alphabetic
characters) to appear in a text message.
MACRO
.VERSION <ARG>
T SET <ARG> ; Set standard symbol to dummy arg
T1 SET ((T.AN.07700).RS.6)+0300 ; 8-bit value of left
T2 SET (T.AN.077)+0300 ; 8-bit value of right half
TEXT /VERSION [T1[T2 OF TEST PROGRAM/
Note that in some sense the `[' operator is the "reverse" of the
single ASCII constant operator. For example, if the value of the
symbol TEMP is 316 (octal), both statements below result in the gen-
eration of the value 316 (octal):
DC TEMP
DC '[TEMP
19.10. Nesting of Macros
Macros may be nested to a level of three. Attempting to call a macro
trhat would increase the nesting depth to four is an error and will
cause the M flag to be posted on the offending macro call. The macro
call would not be processed. A macro may call itself recursively as
long as the nexting level limit is not exceeded.
19.11. Macro Calling Sequences
A typical macro call includes an optional label, the macro name in the
operation code field, any number of real arguments in the operand
field and a comment field.
The label field is passed as a "hidden" argument to the macro and will
be substituted in any label field of the macro body which contains the
lpaired angle brackets.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 32 of 90
Macro arguments are of two types: simple and extended. A simple argu-
ment consists of a string of characters which do not contain a blank,
comma or angle brackets. Angle brackets must not appear in a simple
argument. An extended argument may contain commas and blanks since the
whole argument string is enclosed in angle brackets. All arguments
(simple or extended) must be separated with commas. The extended argu-
ment form is provided primarily to allow nested arguments and to
handle cases where a comma or blank need to be passed as arguments.
Consider these examples:
DEFIN ARG,HELP,TEMP,61,$
ATXT ARG,<THIS IS A TEXT STRING>,ARG2
OUTER ARG,<DEFIN 1,TOOP,TEP,7,90>
NEST <<<ARG,$>>>
In the third case, a macro call with simple arguments is itself passed
as an argument to another macro. In the fourth case, two arguments are
presumably being passed down directly to a macro that is called by
another macro that itself is called within the 'NEST' macro. At each
nesting level in the macro expansions, the outermost pair of angle
brackets associated with that level will be stripped off.
As another example, consider the following macro which repeats some
source statement a specified number of times:
MACRO
.REPEAT <COUNT><STATEMENT>
CT SET <COUNT> ; Set loop counter
.LOOP <STATEMENT> ; Generate the statement
CT SET CT-1 ; Decrement loop counter
AIF CT,.LOOP ; Back if more to do
MEND
This macro could then be called to generate 256 statements of the
form: `ISZ COUNT' with the this call:
.REPEAT 256,<ISZ COUNT>
19.12. Null Arguments
A null argument within the middle of a set of arguments is indicated
by two consecutive commas. If the macro definition has supplied no
default argument in that position, a null string is substituted for
the dummy macrro argument and the # error flag will be posted for the
missing argument. If a default was provided in the macro definition,
the default argument will replace the dummy argument in that position.
In the example below, the third argument in the macro call is null:
DEFN ARG1,HELP,,ARG4,SYM9
19.13. Macro Libraries
The usual way to handle macro libraries is to have a source file
containing the macro definitions assembled in front of other source
files. If only selective portions are required, a file of requests
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 33 of 90
(consisting of equate statements) can be inserted in front of the
macro library. The macro library can then make use of the question-
mark definition operator and conditional assembly branches to skip
macro definitions that are not required.
19.14. Local Macro Symbols
Within a macro it may be necessary to generate unique address labels
on each invocation of the macro. In order to prevent duplicate tag
errors, local macro symbols are used. Although normal local symbols
could be used, serious program errors could arise if a calling routine
was unaware that a particular local symbol appeared in some macro that
was being called. To avoid this difficulty, PAGE8 reserves a set of
special local symbols for each of the three nesting levels. A macro,
local symbol is identical to a normal local prefixed that a $ char-
acter:
MACRO
.EXAMP1
$7H TAD STAK
JMP $2F
NOP
$2H JMP $7B
... ....
Local macro symbols are illegal outside of a macro. Should one be
used, PAGE8 posts the M error flag and uses a normal local symbol
instead. Local macro symbols are only defined at the current nesting
level. Consider the following macro that calls the macro above:
MACRO
.EXAMP2
TAD $2F
.EXAMP1 $2H NOP
....
In this case the $2H tag in .EXAMP2 is not confused with the $2H tag
in .EXAMP1 because they appear at different nesting levels. Also, the
PART directive may be used inside a macro in which case only local
macro symbols at that nesting level are partitioned.
19.15. Character String Processing
The AREAD and MSCAN directives provide PAGE8 with a powerful character
string processing capability. When an AREAD directive is encountered,
PAGE8 reads in the next source statement and treats it as the first
argument to the macro. The first character in the first argument will
comprise the character in column 1 of the statement that was read in
by the AREAD directive.
In conjunction with AREAD, the MSCAN directive makes it possible to
examine each character in the argument one by one and process them
accordingly. MSCAN can also be used on normal arguments thus providing
a way of finding out what type of argument has been supplied to the
macro. For example, a macro could be defined called `OS8TXT' that
would take an argument just like the standard PAGE8 `TEXT' directive.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 34 of 90
The OS8TXT macro could then use the MSCAN cirective to save the deli-
miting character and pick off the characters in the string one by one.
OS8TXT could then use these characters to pack up a message buffer in
the special format required for OS/8 ASCII files.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 35 of 90
20. PAGE8 Directives
20.1. AFIELD (Expression)
Label: Blank or sequence symbol
Operation: AFIELD
Operand: Any expression with a value between 0 and 7
Comment: Permitted
Mnemonic definition: Assembly data FIELD setting.
- -----
This directive specifies the actual run-time data field which will be
in effect for subsequent instructions. This information is used by
PAGE8 to resolve some of the complex field addressing errors that can
appear in a program that is frequently referencing data fields otheer
than the current instruction field. Also, the TADX, ANDX, INCX and
DCAX instructions cause an automatic CDF instruction back to the field
set by the most recent AFIELD directive. If no AFIELD directive has
been issued, PAGE8 sets a continuously updated default of the current
assembly field.
Judicious use of the AFIELD directive can ensure that certain types of
addressing errors will always be caught by PAGE8. For example, if
PAGE8 is forced to generate a paging link for a memory reference in-
struction, the current run-time assembly data field is checked. If
this field differs from the current field, PAGE8 knows that the ref-
erenced location cannot be accessed correctly and will consequently
post the K error flag.
To facilitate field tracing, a macro can be written to force PAGE8 to
change the AFIELD setting whenever a CDF instruction is executed:
UNLINK CDF Remove CDF from op-code tables *
MACRO Now redefine meaning of CDF
CDF <FIELD> ; Argument is 3-bit field
LINK CDF ; recollect CDF definition
!<> CDF <FIELD> ; list & execute CDF with label
UNLINK CDF ; reset `trap' for CDF op-code
AFIELD <FIELD> ; execute implicit AFIELD
MSKIP ; allow skip instruction to precede
MEND
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 36 of 90
20.2. AGO (Sequence Symbol)
Label: Blank or sequence symbol
Operation: AGO
Operand: Sequence Symbol
Comment: Permitted
Mnemonic definition: Assembler GO.
- --
Unconditional assembly branch. The operand field should contain a
sequence symbol to which assembly unconditionally branches. All inter-
vening instructions are not assembled. In a macro, PAGE8 will begin
the search for the matching sequence symbol at the BEGINNING of the
macro, so that a backwards assembly branch is allowed. For this feat-
ure to work correctly, it is important that all sequence symbols with-
in a single macro definition be unique, since the scan always begins
from the first macro body statement. If not in a macro, the sequence
symbol must appear in a subsequent statement. The AGO directive is not
listed unless a prior LISTC directive is in effect.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 37 of 90
20.3. AIF (Expression),(Sequence Symbol)
Label: Blank or sequence symbol
Operation: AIF
Operand: Any expression followed by a sequence symbol
Comment: Permitted
Mnemonic definition: Assembler IF.
- --
Conditional assembly branch. The expression in the operand field is
evaluated. If it has a non-zero value (i.e. TRUE), the assembly branch
will be taken as if an AGO directive had been issued to the specified
sequence symbol. If the expression has a zero value (i.e. FALSE), the
assembly branch is not taken and the AIF directive functions as an
ANOP directive. As with the AGO directive, backwards assembly branches
are permitted within macros.
If the expression in the operand field was false, the AIF statement is
listed. If the expression was true and the assembly branch taken, the
AIF statement is not listed unless a LISTC directive is in effect.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 38 of 90
20.4. ALIGN
Label: Blank or sequence symbol
Operation: ALIGN
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: ALIGN to start of next memory page.
-----
Unconditional page alignment. When encountered, PAGE8 will force ali-
gnment to the start of the next PDP-8 memory page. This directive is
similar in function to the PAGE directive of the PAL8 assembler
although it rarely appears in PAGE8 programs. The current page literal
pool is output and a page escape is generated in the normal manner.
If the next page has been marked as unavailable by a prior GAP dir-
ective and if the current program section is in ISEC 0, PAGE8 will
align to the start of the next available page in that memory field and
adjust the linkage in the page escape. If there are no further avail-
able pages, the K error flag is posted and assembly continues at
location 0000 in the next memory field.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 39 of 90
20.5. ANOP
Label: Blank or sequence symbol
Operation: ANOP
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: Assembly NO-oP.
- -- -
This directive has no function other than to service as a target oper-
ation code for a sequence symbol in the label field. This is generally
used in conjunction with the AGO and AIF directives. No object code is
generated by this directive.
The ANOP directive can also be used to separate operation codes which
might generate some unwanted error flag if they occurred as con-
secutive statements. For example, it is illegal to have two con-
secutive TEXT directives in an ISEC area due to the possibility of a
semantic error (viz. an unexpected and undesirable page break could
occur between the two text strings). In this case, the restriction can
be easily overcome by simply inserting an ANOP statement between the
two TEXT directives.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 40 of 90
20.6. AREAD
Label: Blank or sequence symbol
Operation: AREAD
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: Assembly READ.
- ----
This is a macro directive which causes PAGE8 to read in the next
source statement as a single, extended argument to the current macro
that is being expanded. All characters of the following statement are
read in and can then be processed by the macro. This directive is
generally used in conjunction with the MSCAN directive in order to
provide PAGE8 with a complete character string processing capability.
The statement to be read does not have to be a PAGE8 statement--it can
have any syntax or form since the statement would only be interpreted
by the macro that issued the AREAD directive.
The example below may help to clarify the use of this directive. This
macro is passed an argument indicating the number of folowing source
statements that comprise a single block of text:
MACRO
.TBLOK <ARG> ; Argument is # of statements
COUNT SET <ARG> ; Set up loop counter
.LOOP AREAD ; Read next source statement
TEXT /<ARG>/ ; `ARG' contains statement
COUNT SET COUNT-1 ; Decrement loop counter
AIF COUNT,.LOOP ; Loop back if more
MEND ; Else all done
*
* Example of a call to the above macro
*
.TBLOK 3 Three source statements
THIS IS THE FIRST STATEMENT TO BE PROCESSED HERE
%$#*@& IT DOESN'T HAVE TO BE A LEGAL PAGE8 STATEMENT*&#@
----------THIS IS THE FINAL STATEMENT----------
*
* Normal PAGE8 statements continue now
*
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 41 of 90
20.7. AS (Expression),(Expression)
Label: Syymbol, sequence symbol or blank
Operation: AS
Operand: An expression, followied by an optional ex-
pression
Comment: Permitted
Mnemonic definition: Allocate Storage.
- -
The AS directive provides a convenient method of allocating large
blocks of storage in a program. The expression in the operand field is
evaluated and treated as the length of a block of storage that should
be reserved starting at the current location. In an ISEC area, if
there is no room on the current PDP-8 page, the block will be aligned
to the start of the next page. If there is a label field, the label
will refer to the address of the first location in the block. All
locations in the block will be set to the value of the second expres-
sion. If the second expression is omitted, a default value of zero is
used to fill the block.
The first expression must contain only previously defined symbols.
This restriction does not apply to the optional second expression. A
large storage block will not be broken up to skip over pages marked as
unavailable because of a prior GAP directive. The block will, however,
not start at the beginning of an object gap.
The example below will generate a block of 128 words where each word
will contain the value -1:
TABLE AS 128,-1 Entire table set to -1
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 42 of 90
20.8. BYTE (Expression),(Expression)
Label: Symbol, sequence symbol or blank
Operation: BYTE
Operand: Two expressions each in the range 0-63 (deci-
mal)
Comment: Permitted
Mnemonic definition: BYTE constant.
----
The operand to the BYTE directive must be two 6-bit expressions sep-
arated by a comma. The first expression goes in the left byte (i.e.
left 6 bits of the word) and the second expression in the right byte.
If either expression is larger than 63 (decimal), the T error flag
will be posted to indicate a truncate error and the value for that
expression will be truncated to 6 bits.
In the example below, the BYTE directive is used to implement a trans-
late table where the right byte contains the translated value and the
left byte contains control and status flags:
BYTE ALPHA,"@A
BYTE DIGIT,"@6
BYTE SPECIAL+ILLEGAL,"@#
BYTE SPECIAL,"@$
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 43 of 90
20.9. CREF
Label: Sequence symbol or blank
Operation: CREF
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: accumulate Cross REFerences.
- ---
The CREF directive allows the accumulation of cross- references to
symbols to resume immediately. If no prior NOCREF directive was in
force, the CREF directive has no effect and functions as an ANOP
directive.
The CREF and NOCREF directives are often encountered in macro defini-
tions that incorporate loops. Such macros can genedrate extraordinary
quantities of cross-references that may be of no use or significance
to the programmer.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 44 of 90
20.10. DC (Expression),(Expression),(Expression),...
Label: Symbol, sequence symbol or blank
Operation: DC (optional)
Operand: An expression followed by optional sub-ex-
pressions
Comment: Permitted
Mnemonic definition: Define Constant.
- -
The DC directive provides a convenient was of specifying single con-
stants or multiple constant lists. The first expression in the operand
field is evaluated and stored at the current location. This first
expression may be a literal. Optional multiple expression separated by
commas are allow to follow and will be stored in successive locations.
These sub-expressions may not contain literals.
A label, if present, will always refer to the address of the first
constant in the string. Multiple expressions are guaranteed to stay
together as a unit--a page break cannot occur within the list of con-
stants.
Pagination recalculations are not performed on any expressions in the
string. Also, all expressions are evaluated prior to generation of any
object code, so that references to the current assembly location coun-
ter lin a sub-expression will reference the address of the first con-
stant rather than the address of the constant that contains the refer-
ence.
Note that the use of `DC' in the operation code field is optional.
PAGE8 first tests the operation code field for a standard PAGE8 opera-
tion code. If this failes, PAGE8 tests to see if it is a macrfo. If it
is not a macro, PAGE8 defaults the operation code to `DC' and then
rescans the operation code field as an operand field to `DC'. The two
statements below are equivalent in PAGE8:
TAG DC 4*3+(TEMP/14)
TAG 4*3+(TEMP/14)
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 45 of 90
20.11. DI (Expression)
Label: Symbol, sequence symbol or blank
Operation: DI
Operand: Any valid expression
Comment: Permitted
Mnemonic definition: Define Instruction constant.
- -
This directive is essentially identical to the DC directive. It is
provided merely for syntactic clarity in the source program and in-
dicates that the constant in the operand field is an instruction to be
executed rather than data. For instruction constants that may cause a
skip, see the definition of the DSI diredctive.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 46 of 90
20.12. DSEC
Label: Sequence symbol or blank
Operation: DSEC
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: Data SECtion.
- ---
This directive indicates that all the following statements comprise a
data section in the program. Genration of automatic page escapes is
inhibited and no pagination recalculations will be performed. When
this directive is encountered, PAGE8 will perform a page alignment and
output the current page literal pool only if some paging links or
literals have been generated on the current memory page. Otherwise no
page alignment will occur. The DSEC directive has no effect on the
current ISEC area. DSEC is essentially a sub-section of an ISEC area.
Instructions used in a DSEC area will be processed correctly. However,
all paging links and literals will be forced into the page zero lit-
eral pool rather than the current page literal pool. This occurs even
if the explicit current page literal operator (=) is used in the
operand field. This feature can be very useful when space is at an
absolute premium, since sharing of all literals and links on page zero
increases the packing density of the program.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 47 of 90
20.13. DSI (Expression)
Label: Symbol, sequence symbol or blank
Operation: DSI
Operand: Any valid expression
Comment: Permitted
Mnemonic definition: Define Skip Instruction constant.
- - -
This directive is essentially identical to the DI directive. The dif-
ference lies in the fact that DSI informs PAGE8 that the instruction
constant to be assembled may cause a skip when it is executed. This
information is needed by PAGE8 to ensure that a page break does not
occur immediately after this instruction. If there is not enough room
on the current page to hold the following instruction, PAGE8 will
force a page alighment and assemble the instruction on the next avail-
able page.
The example below shows a very common usage of the DSI instruction.
Note that using DC instead of DSI could result in a bad page break in
some future assembly.
SWITCH DSI 07000 NOP now, may be a skip later on
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 48 of 90
20.14. EJECT (Expression)
Label: Sequence symbol or blank
Operation: EJECT
Operand: Blank or an optional expression
Comment: Permitted
Mnemonic definition: EJECT page.
-----
PAGE8 performs an explicit page eject on the output device before
listing the following statement. The EJECT directive is not listed.
If the operand field contains an expression, the EJECTG directive
becomes conditional: a page eject wsill only occur if the curfrent
line lies within the specified number of lines of the bottom of the
page. This conditional form of the directive can be very useful in
obtaining clean, readable listings of the source program. Note also
that through the use of the equals (=) run-time option, all uncondi-
tional page ejects can be forced to be conditional to a specific
value.
In the example below, a condition EJECT directive is used to ensure
that the description of a subroutine does not get separated from the
entry to the subroutine:
EJECT 10 Do an eject if less than 10 lines left
* * The calling convention for
this subroutine........ *
SUBR SUB
..........
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 49 of 90
20.15. END
Label: Sequence symbol or blank
Operation: END
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: END of source program.
---
This directive signifies that assembly should terminate with this
statement. Use of this directive is optional. If PAGE8 reaches the
end-of-file in the last sourced file, PAGE8 will terminate the
assembly pass normally as if an END directive had been elxplicitly
issued.
The primary use of this directive is for conditional assemblies where
it may be desirable to mark the end of the program without having to
include an assembly branch over any remaining source statements.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 50 of 90
20.16. (Symbol) EQU (Expression)
Label: Symbol
Operation: EQU
Operand: Any valid expression
Comment: Permitted
Mnemonic definition: EQUate symbol.
---
The symbol in the label field is equated to the value of the expres-
sion in the operand field. As with the QUT directive, any attempts to
redefine the symbol with a difference value will be treated as an
error (the SET directive should be used lif redefinition is required).
Note that EQU is not generally used for equating symbolic add-
resses--the QUT directive is used for that purpose. However, if sym-
bolic addresses are defined with the EQU directive, any references to
that symbol will be assumed to be in the current memory field. This
feature can be useful on occasion. For example, it may be desirable to
equate the addresses of some cells which are present at the same rel-
ative location within each memory field (viz. general gemporary or
"garbage" cells). Such symbols can then be referenced in any memory
field without generation of a K field addressing error.
The operand field may not contain any symbols which are defined at a
later point in the source program. Should lthis occur, the Q error
flag will be posted and the expression will always have a value of
zero. Illegal forward references do not cause assembly phase errors in
PAGE8.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 51 of 90
20.17. ERM
Label: Sequence symbol or blank
Operation: ERM
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: End RooM check.
- - -
This directive is used in conjunction with the ROOM directive. If the
statement lies outside of the protected range set by a ROOM directive,
the square bracket error flag (illegal unprotected statement) will be
posted. If protected, the ERM directive functions like an ANOP dir-
ective.
The ERM directive is useful when it becomes necessary to protect a
large number of statements. Because of the complex nature of the ROOM
directive and the necessary prohibition of future references, it is
not always easy to tell how large the operand to the ROOM directive
should be until an assembly listing is generated. The ERM directive
provides a convenient way of ensuring that the ROOM directive preced-
ing this statement does indeed protect the necessary number of state-
ments against a page break.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 52 of 90
20.18. ERROR: (User-defined error message)
Label: Sequence symbol or blank
Operation: ERROR:
Operand: User-defined text for an error message
Comment: Continuation of the operand field
Mnemonic definition: ERROR message.
-----
This directive makes it possible to signal user-defined error messages
during assembly of a program. When encountered, PAGE8 posts the error
asterisks and forces the listing of the statement just as if a valid
error flag had been posted internally by PAGE8. The operand and com-
ment field to the directive will normally contain an error message
that identifies the error condition that was detected during assembly
of the program. The error will also appear in the cross-reference
directory of errors, with a blank for the posted error flag.
This directive provides an extremely useful tool for protecting pro-
grams during future assemblies or source modifications. Coupled with
the use of conditional assembly directives, checks can be made for all
kinds of special error conditions in a source program. For example,
one can check that a program lies within certain memory limits, or
check that tables have the correct length. It is also very useful in
macros. Often the macros will have been written by another programmer
who can then include checks that the arguments passed to the macro
have the correct form or type, or that the correct number of arguments
are passed.
See also use of the NOTE: directive which has a somewhat similar
function. In the example below, a macro checks that the first argument
to be passed has a value of 5 or less:
MACRO
.SAMPLE <ARG1><ARG2> ; 2 arguments to the macro
AIF <ARG1>.LE.5,.OK ; Assembly branch if legal
ERROR: <ARG1> IS INVALID--IT SHOULD BE 5 OR LESS!
.OK ANOP
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 53 of 90
20.19. FIELD (Expression)
Label: Sequence symbol or blank
Operation: FIELD
Operand: Any expression whose value lies between 1 and
7
Comment: Permitted
Mnemonic definition: FIELD address.
-----
This directive indicates to PAGE8 the memory field at which assembly
is to continue. It is similar to the ORG directive in that the expres-
sion field must not contain any symbols that are defined at a later
point in the source program. Should this occur, thed Q error flag will
be lposted and the FIELD directive will be ignored in all assembly
passes (an assembly phase error does not occur).
Also, field settings may not go backwards, the operand field must
contain a value that is greater and not equal to the current field
setting. If an attempt is made to set the field backwards, the B error
flag will be posted and the FIELD directive will be ignored.
When the FIELD directive is encountered, the current page literal pool
is output followed by the page zero literal pool. No page escape is
generated and the assembly location counter is reset back to zero.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 54 of 90
20.20. FILE (Source program name)
Label: Sequence symbol or blank
Operation: FILE
Operand: Character string of up to 40 characters
Comment: Treated as an extension of the operand field
Mnemonic definition: FILEname for mail title.
----
The FILE directive should be followed by a character string of no more
than 40 characters which will then be used as the main title on line 1
of the assembled source listing. The title begins with the first non-
blank character in the operand field. The FILE directive will cause a
page eject to be performed before listing the next statement. If the
character string exceeds 40 characters in length, it will be truncated
to that length without any error message.
PAGE8 assumes that the first source statement will contain a FILE
directive. If it is omitted, and the first statement is not TITLE or
EJECT, the first line in the source file will not be listed properly
(it will be listed by itself prior to the first page). The FILE dir-
ective may actually appear anywhere in the source program. It is not
restricted in use to the first statement in the source file and it may
be used any number of times within a source file.
Generally, PAGE8 programs use this directgive at the start olf each
source file, so that one can tell immediately from the listing what
the name of the associated source file is. See also use of the TITLE
directive which is normally used for providing sub-headings within a
source file.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 55 of 90
20.21. FREE (Expression)
Label: Sequence symbol or blank
Operation: FREE
Operand: Expression in the range 0-63 (decimal)
Comment: Permitted
Mnemonic definition: FREE up room on page.
----
This directive contains an operand field which specifies the minimum
number of free locations to be reserved at the end of each PDP-8
memory page. The default value set by PAGE8 at the beginning of each
pass is zero, indicating that most memory pages will be completely
packed. This directive may appear anywhere and any number of times
within the source program.
This directive is particularly useful during the debugging stages of a
program. With this directive, the programmer can ensure that there is
plenty of room on each page for patching purposes. Once debugged, the
FREE statement can be removed, thus restoring the optimal packing
density for the program.
Note that this directive specifies the minimum number of free loca-
tions to be reserved. Because of the way in which instructions are
assembled, it is entirely possible that one or two extra locations
will be left free. This can happen when a skip instruction occurs
right at the end of a page, or when some expressions that were undefi-
ned in pass 1 are found to resolve to the same entry in the literal
lpool during subsequent passes.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 56 of 90
20.22. GAP (Expression),(Expression),(Expression)
Label: Sequence symbol or blank
Operation: GAP
Operand: Three expressions separated by commas
Comment: Permitted
Mnemonic definition: object GAP.
---
This is a highly unusual assembly directive that is provided to
enhance the usefulness of the automatic paging feature of PAGE8. This
directive is followed by three expressions in the operand field. The
first expression will contain the field address of the gap as value in
the range 0-7. The second expression will contain the 12-bit starting
address of the object gap, and the third expression will contain the
number of words in the gap. The latter two expressions should be
multiples of 128 (e.e. on a page boundary). Object gaps may not lie
below location 0400 in a field.
During automatic pagination of the source program, PAGE8 checks to see
if the next page lies within a specified object gap. If it does, the
page(s) specified in the gap are skipped over and assembly continues
at the first free page after the gap. This skipping over object gaps
only occurs in ISEC 0. In ISEC area 1, object gaps are always ignored.
When skipping over an object gap, PAGE8 adjusts the final entry in the
previous page's literal pool to ensure that the paging link correctly
jumps over the object gap. This means that the programmer can reserve
pages at the beginning of the program without having to be concerned
about overlaying them with subsequent source code. There is room for
the specification of 4 object gaps in each of the 8 memory fields. The
Y error flag will posted if this limit is exceeded.
This directive can be useful for reserving data space at specified
locations within a program. Also, these object gaps can be filled in
later with code by switching to ISEC 1 and setting the origin to the
start of the object gap.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 57 of 90
20.23. ISEC (Expression)
Label: Sequence symbol or blank
Operation: ISEC
Operand: Expression with a value of 0 or 1
Comment: Permitted
Mnemonic definition: Instruction SECtion.
- ---
The operand field must contain an expression who value is either zero
or one in order to select on of the two instruction sections. Each
instruction section has its own set of location counters (12-bit loca-
tion counter, field location counter and AFIELD location counter).
PAGE8 defaults to instruction section 0 at the start of each pass.
When switching between instruction section areas, a page break is
forced in the old ISEC area (if necessary) and the saved assembly
location counters for the new area are loaded. Two instruction sec-
tions are provided in order to overcome the restriction in PAGE8 of
setting an origin backwards. If there is a need to go backwards, a
switch can be made to the other instruction section whose location
counters have not been affected.
Extreme caution is required in the correct handling of this feature.
In particular, problems can arise in switching between ISEC areas
where the assembly fields are different. In general, both ISEC areas
should be updated at the same time. The reason for this is that when
switching between ISEC areas, the page zero literal pool is not out-
put. This could cause literals from both fields to be stored in the
same pool. The page zero literal pool is not output in order to make
it possible to briefly switch instruction sections and back again
without losing all the page zero literals.
In most cases, the programmer will find that it is best either to
update fields in both areas at the same time, or to only switch sec-
tions once in a program, preceding the instruction section switch with
a FIELD directive to ensure that the page zero literals are output in
the correct memory field.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 58 of 90
20.24. LFIELD (Expression)
Label: Sequence symbol or blank
Operation: LFIELD
Operand: Expression in the range 0-7
Comment: Permitted
Mnemonic definition: Load FIELD.
- -----
The operand field should contain an expression in the range of 0-7.
The field setting is punched on the object code during pass2. Neither
the current assembly field nor the location counter are reset and the
page zero literals are not affected.
On the listing, all the addresses will have an asterisk posted after
them to indicate that the actual address on the listing differs from
the address at which the assembled object code will be loaded.
Relocation of the object code will remain in effect until an ORG or
FIELD directive is encountered. Either of these directives will remove
the relocation. See also the use of the LOAD directive which effects
relocations within a memory field.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 59 of 90
20.25. LINK (Operation code)
Label: Sequence symbol or blank
Operation: LINK
Operand: Any PAGE8 operation code
Comment: Permitted
Mnemonic definition: LINK definition.
----
The LINK directive causes the referenced operation code to be inserted
back into the PAGE8 operation code tables. If it is already in the
table, this directive has no effect and functions as an ANOP.
The LINK directive is generally used within a macro who function is to
trap out some standard PAGE8 operation code in order to provide some
extra feature.
The example below should clarify the use of the LINK and UNLINK dir-
ectives. This macro traps out the LIST directive in order to get the
directive listed (PAGE8 normally suppresses the listing of this dir-
ective) and also assert a LISTC directive as well:
UNLINK LIST Set trap on LIST directive in main
code
*
MACRO Macro to process trapped LIST
LINK LIST ; Recollect standard definition
LIST ; Turn on the listing
UNLINK LIST ; Set `trap' again
LISTC ; Turn on conditional list, too
! ANOP ; `LIST' gets listed here
MSKIP ; Allow a preceding skip instruction
MEND
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20.26. LIST
Label: Sequence symbol or blank
Operation: LIST
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: turn on LISTing.
----
The LIST directive controls the listing output. If the listing had
been turned off by a previous NOLIST directive, the listing is now
turned back on. If the listing was currently on, this directive has no
effect. The LIST directive is not listed by PAGE8.
The LIST directive will not override the effect of the /L run-time
option (which turns the listing off permanently).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 61 of 90
20.27. LISTC
Label: Sequence symbol or blank
Operation: LISTC
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: LIST Conditional source.
---- -
The LISTC directive controls the listing of statements that are not
being assembled (dur to a prior AGO or AIF directive). This directive
has the effect of causing the unassembled statements to be listed.
PAGE8 defaults to a NOLISTC condition at the start of each assembly
pass. The LISTC directive is not listed.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 62 of 90
20.28. LISTM
Label: Sequence symbol or blank
Operation: LISTM
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: LIST Macro expansion.
---- -
The LISTM directive specifies that the source code generated during
the expansion of a macro should be listed along with the macro call.
PAGE8 defaults to a NOLISTM condition at the start of each assembly
pass.
This directive is generally used during debugging of complex macro
definitions or in cases where the macro definition itself supplies
useful documentation.
The LISTM directive is not listed.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 63 of 90
20.29. LOAD
Label: Sequence symbol or blank
Operation: LOAD
Operand: Any PAGE8 expression
Comment: Permitted
Mnemonic definition: LOAD origin.
----
The LOAD directive specifies that the following object code should be
loaded at the address indicated by the expression in the operand
field. This origin setting in punched on the object code output during
pass 2. As with the LFIELD directive, the current assembly location
counter is not affected, nor is the current page literal pool output.
An asterisk will appear after the address field on the listing to
indicate thatg relocation is in effect. PAGE8 adds the relocation
constant (i.e. difference between load and assemblyu origins) when
outputting the origin for the current page literal pool, so that cur-
rent page literals and links are addressed correctly even when reloca-
tion is in effect. The programmer should be aware, however, that the
page escape and other paging links reflect values relative to the
current location counter and not the address at which the object code
will be loaded.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 64 of 90
20.30. MACRO
Label: Sequence symbol or blank
Operation: MACRO
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: MACRO definition.
-----
This directive indicates that all subsequent statements up to the fol-
lowing MEND directive comprise a macro definition. The next stgatement
after the MACRO directive will be the prototype header statement which
contains the name of the macro and the format of the arguments that
will be passed to the macro.
All subsequent body statements will be treated as part of the macro
definition until the MEND directive is found, at which point the macro
definition will be terminated. Although macro calls can be nested,
macro definitions may not be nested, nor may a macro be defined with a
macro.
A detailed description of macros and macro definitions will be found
in the section: PAGE8 MACRO PROCESSOR 19. (Pg. 25).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 65 of 90
20.31. MEND
Label: Sequence symbol or blank
Operation: MEND
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: Macro definition END statement.
- ---
This directive indicates the end of a macro definition. It also ter-
minates the expansion of the macro definition when the macro is being
processed. If this directive appears without a prior MACRO directive,
the M error flag will be posted (macro syntax error).
Conditional or unconditional assembly branches are not permitted
across a MEND statement. If the assembly is off when the MEND dir-
ective is found, the assembly is automatically turned back on again
without generating an error message.
More details on the use of macro directives can be found in the
secion: PAGE8 MACRO PROCESSOR 19. (Pg. 25).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 66 of 90
20.32. MEXIT
Label: Sequence symbol or blank
Operation: MEXIT
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: end Macro expansion and EXIT macro.
- ----
When encountered during the expansion of a macro, PAGE8 terminates the
expansion with this statement. MEXIT is identical to MEND except that
it does not mark the end of a macro definition. MEXIT is provided to
allow premature exits from the macro expansion without having to use
assembly branches to the MEND statement.
More details on the use of macro directives can be found in the
secion: PAGE8 MACRO PROCESSOR 19. (Pg. 25).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 67 of 90
20.33. MONR
Label: Sequence symbol or blank
Operatin: MONR
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: MONitor Return.
--- -
When the directive is encountered, PAGE8 immediately returns to the
OS/8 monitor program by executing a JMP to location 07600. The purpose
of this directive is to allow assembly to be aborted immediately in
the event of some fatal error lcondition. It is generally used in
conjunction with the ERROR: and NOTE: directives.
For example, a program can check to see if it is using too much
memory. If is it (and this is an absolutely hopeless error condition),
the program can use the AIF directive to perform the check, the ERROR:
directive to inform the user of the error condition and the MONR dir-
ective to force an immediate abort of the assembly. This can be
especially useful when PAGE8 is running under OS/8 BATCH.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 68 of 90
20.34. (Symbol) MSCAN (Expression),(Dummy macro agrument)
Label: Symbol
Operation: MSCAN
Operand: An expression followed by a dummy macro argu-
ment
Comment: Permitted
Mnemonic definition: Macro argument character SCAN.
- ----
This directive makes it possible to examine a single character in an
argument (usually a substitution for a dummy macro argument) and
obtain the value of the ASCII character code for that character. lThe
character in the argument to be "scanned" is specified by the first
expression. For example, if the argument begins with the letter `A'
and the first expression has a value of zero, the symbol will be set
to the value of 301 (octal) (the ASCII character code for the letter
`A'. If the first expression had a value of 7, the 8th character in
the string would be returned.
This directive provides PAGE8 with a powerful character string proces-
sing capability. The example below should help to clarify its use.
This macro reads a string of characters until a carriage return code
is found and then generates an ASCII text string where each character
is stored right-justified, one character per word.
MACRO
.ASCII <STRING> ; Argument is character string
PTR SET 0 ; Initialize character pointer
.LOOP ANOP ; Loop here for next character
CHAR MSCAN PTR,<STRING> ; Pick off next character
AIF CHAR.NE.0215,.GO ; If CR, we are done
MEXIT ; It was CR, all done
.GO DC CHAR ; Generate the character
AGO .LOOP ; Loop back for next character
MEND
To call the macro above, the text string would be passed as a single,
extended argument (to avoid problems with blanks).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 69 of 90
20.35. MSKIP
Label: Sequence symbol or blank
Operation: MSKIP
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: Macro SKIP permitted.
- ----
This is a macro directive that inhibits PAGE8 from posting the "Il-
legal Unprotected Statement" flag if it finds that the macro call is
preceded with a skip instruction.
It is often very easy to forget that a macro may generate a sub-
stantial amount of object code from a single statement calling the
macro. PAGE8 accomodates this common mistake by posting an error flag
if it finds a macro call preceded with a skip instruction.
Some macros, however, may not generate any object code, or may gen-
erate only one instruction. In these cases, it would be permissable to
precede the macro call with a skip instruction without having an error
flag posted. By including the MSKIP directive at some point within the
macro definition, PAGE8 will not execute the check for a preceding
skip instruction when the macro call is encountered and will not post
the error flag. Note that the MSKIP directive can appear anywhere in
the macro definition--its position is not important.
More details on the use of macro directives can be found in the
secion: PAGE8 MACRO PROCESSOR 19. (Pg. 25).
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 70 of 90
20.36. NOCREF
Label: Sequence symbol or blank
Operation: NOCREF
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: NO Cross-REFerences.
-- - ---
The NOCREF directive inhibits the accumulation of cross-references to
symbols until a later CREF directive is encountered. This directive is
normally used in macros that contain iterative code. Use of this dir-
ective inbigits generation of hundreds or possibly thousands of cross-
references which are of no significant value.
PAGE8 defaults to a CREF condition at the start of each assembly pass.
The NOCREF cirective does not affect cross-reference accumulation of
definitions. In particular, if a symbol is being constantly redefined
with SET, references will still appear in the cross-reference dir-
ectory even if NOCREF is in effect.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 71 of 90
20.37. NOLIST
Label: Sequence symbol or blank
Operation: NOLIST
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: NO LISTing.
-- ----
The NOLIST directive controls the listing of the assembled program. If
the listing was on, the listing is not turned off. If the listing was
curfrently off, then this directive has no effect. The NOLIST dir-
ective is not listed.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 72 of 90
20.38. NOLISTC
Label: Sequence symbol or blank
Operation: NOLISTC
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: do NOt LIST Conditional source.
-- ---- -
The LISTC directive controls the listing of statements that are not
being assembled because of a prior AGO or AIF directive that turned
off the assembly. When a NOLISTC directive has been encountered, PAGE8
will not list statements that are not being assembled.
PAGE8 defaults to a NOLISTC condition at the start of each assembly
pass.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 73 of 90
20.39. NOLISTM
Label: Sequence symbol or blank
Operation: NOLISTM
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: do NOt LIST Macro expansions.
-- ---- -
The NOLISTM directive specifies that only the assembled object code
and macro call are to be listed during the expansion of a macro.
NOLISTM cancels the effect of a prior LISTM directive.
PAGE8 defaults to a NOLISTM condition at the beginning of each
assembly pass.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 74 of 90
20.40. NOTE: (User-defined message)
Label: Sequence symbol or blank
Operation: NOTE:
Operand: Contains a user-defined text message
Comment: Treated as a continuation of the operand field
Mnemonic definition: print NOTE.
----
This directive is identical to the ERROR: directive except that no
error condition is signalled. The error asterisks do not appear, and
no entry appears in the cross reference cirectory of errors. However,
the listing will be forced on, to ensure that this statement is list-
ed. If will be printed during each pass when the statement is encoun-
tered.
The passes one and two, the message will always appear on the master
terminal. In pass 3, the message will appear on the third pass list
file.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 75 of 90
20.41. ORG (Expression)
Label: Sequence symbol or blank
Operation: ORG
Operand: Any valid PAGE8 expression
Comment: Permitted
Mnemonic definition: ORiGin setting.
-- -
The ORG directive sets the origin for subsequent assembly. The expres-
sion in the operand field is evaluated and becomes the new origin for
continuation of the assembly. A default origin of zero is assigned by
PAGE8 at the beginning of each pass, or whenever a FIELD directive is
encountered. If the origin is set backwards within a given ISEC area,
the B error flag will be posted, and a HLT instruction assembled
instead. A HLT instruction is assembled in order to force generation
of object code so that the current location counter will be printed
along with the flagged statement. This feature provides a convenient
wasy of checking that a program does not go beyond a certain memory
address.
Any symbols in the operand field must have been previously defined in
a prior source statement or the Q error flag will be posted and the
origin will not be changed. This action takes place in all passes so
that no assembly phase errors will occur.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 76 of 90
20.42. PAGE
Label: Sequence symbol or blank
Operation: PAGE
Operand: Expression in the range 0-127 (decimal)
Comment: Permitted
Mnemonic definition: PAGE depth.
----
This directive is used to control the number of lines to appear on
each page of the listing generated during pass 3. The operand field
should contain an expression indicating the required number of lines.
PAGE8 defaults to a page depth of 52 lines per page at the start of
each assembly pass.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 77 of 90
20.43. PART
Label: Sequence symbol or blank
Operation: PART
Operand: Treated as part of the comment field
Comment: Permitted
Mnemonic definition: PARTition local symbols.
----
When a PART directive is found, PAGE8 ensures that no previous for-
ward, nor following backward local symbols "cross" this statement. Any
attempts to reference a local symbol across a PART directive will
cause the U error flag (unedfined symbol) to be lposted. If in a macro
expansion, local macro symbols at the current nesting level are par-
titioned.
This directive is supplied in order to combat the difficulties that
arise when a local symbol tag is missing: no error flag is posted and
the reference will go forward or backwards until a tag is found with
the same number. Obviously, there is no way that PAGE8 can determine
that a local symbol tag is missing. However, by including frequent
PART directives in a program, the programmer can guard against this
problem quite effectively.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 78 of 90
20.44. PUNCH (Expression)
Label: Sequence symbol or blank
Operation: PUNCH
Operand: Any valid PAGE8 expression
Comment: Permitted
Mnemonic definition: PUNCH object code.
-----
The PUNCH directive specifies that the 8-bit value of the expression
in the operand field is to be punched on the pass 2 object code with-
out updating the assembly location counter. The 8-bit value is added
into the binary checksum. If the value is greater than 8 bits, it is
truncated to 8 bits without any error flag's being posted.
By specifying a value with bit zero set (i.e. by adding the constant
4000 (octal)), the low order 8 bits will be punched as above but the
value will NOT be added into the binary checksum. lThis directive
caters to special loading programs other than ABSLDR or the standard
paper tape binary loader. For example, the DEC typesetting loader has
a special DECtape origin indication--DTORG. A macro can be easily
written using the PUNCH directive to generate the special format
needed by that loading program.
As a cross-assembler, macros incorporating the PUNCH directive can
generate special record headers, trailers, data formats and checksums
for the object loader programs that run on that compouter. Macros can
even be written to take an object byte and output it is a highly
specialized format such as the BPNF standards require for burning
ROMs.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 79 of 90
20.45. (Symbol) QUT (Expression),(Expression)
Label: Symbol
Operation: QUT
Operand: Expression in range 0-7, followed by an ex-
pression
Comment: Permitted
Mnemonic definition: eQUaTe to address.
-- -
The operand field should contain two expressions separated by a single
comma. The first expression should be the 3-bit field address for the
symbol in the range 0-7. The second expression should contain the
12-bit address within that field for the symbol. Offset references to
symbols defined by QUT will be adjusted (if necessary) by the pagina-
tion routines. In other words, QUT defines a symbol in the same way
that it would have been defined if the symbol had appeared in the
label field at the specified address.
Note that the external symbol directory generated by the /D or /G run-
time options defines all the symbolic addresses in terms of QUT state-
ments. Offset references, however, should be used with great care
since PAGE8 does not have access to the page mapping tables that were
built during the previous assembly. To be safe, offset references
should probably be avoided altogether when referencing symbols defined
through an external symbol directory.
See also the use of the EQU directive for defining symbolic addresses,
since the EQU directive has some special features associated with its
use in defining addresses.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 80 of 90
20.46. RADIX (Expression)
Label: Sequence symbol or blank
Operation: RADIX
Operand: An expression in the range 2-10 (decimal)
Comment: Permitted
Mnemonic definition: RADIX setting for untyped constants.
-----
This directive sets a new radix in the range of 2-10 (decimal) for
untyped constants. All following untyped constants will be evaluated
in this specified radix. Radix settings do not affect the use of a
precedent zero on untyped constants as an alternate way of expressing
octal constants--a leading zero always specifies an octal constant.
Also, the sign change warning posted on untyped constants applies only
to decimal constants.
This directive should be used with care. In particular, failure to
reset the radix back again after its use could cause very obscure
errors in a program. Also, the operand field for the RADIX directive
should use a typed constant, since the current radix of untyped con-
stants may not be known at that point. PAGE8 will always check that
all digits used in an untyped constant lie within the radix specified
by the RADIX directive.
PAGE8 defaults to a radix of 10 (decimal) at the start of each
assembly pass.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 81 of 90
20.47. RET
Label: Symbol, sequence symbol or blank
Operation: RET
Operand: Any expression containing a symbolic address
Comment: Permitted
Mnemonic definition: RETurn from subroutine.
---
The RET directive provides the normal way of exiting from a subroutine
whose entry point has been defined with the SUB directive. If the
subroutine entry point is on the same page as the RET, an indirect JMP
instruction is assembled through the entry point to the subroutine. If
the RET is on a different page, an indirect JMP is assembled through a
paging link that points one location back from the subroutine entry
point. In these cases, it will require two jumps to exit from the
subroutine.
The operand field to the RET directive must contain a symbolic address
which appeared in the label field of a SUB directive. If PAGE8 fiends
that this is not the case, the J error flag is posted. See also the
description of the SUB directive and the section on SUBROUTINES.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 82 of 90
20.48. ROOM (Expression)
Label: Sequence symbol or blank
Operation: ROOM
Operand: An expression in the range 0-63 (decimal)
Comment: Permitted
Mnemonic definition: ROOM on page.
----
The ROOM directive takes an operand field which specifies the number
of following locations which must be assembled together on a page.
PAGE8 forces a premature page break if necessary. Prior definition of
any symbols in the expression is required or the Q error flag will be
postged and the directive will be ignored.
Because of the complex nature of the ROOM directive, PAGE8 posts
status flags on the listing to show approximately how many instruc-
tions (or data) are covered by the ROOM directive. As a simply (al-
though not totally accurate) guide, the following "rule" can be app-
lied:
1 for data,
2 for instructions,
1 additional if the last instruction is a skip.
Following this rule will guarantee proper coverage. In point of fact,
this "rule" will often result in an unnecessarily high value since
certain instructions (operates and page zero memory reference) will
generally only require one location. On the other hand, current page
references may require one or two locations depending on where the
pages break, so it is probably best to use the conservative rule
above.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 83 of 90
20.49. (Symbol) SET (Expression)
Label: Symbol
Operation: SET
Operand: Any valid expression
Comment: Permitted
Mnemonic definition: SET value of symbol.
---
The SET directive is identical in function to the EQU directive except
that SET allows the symbol in the label field to be redefined to a
different value withoput generation of an error condition. The expres-
sion in the operand field is evaluated and assigned to the current
value of the symbol in the label field and the old value (if any) is
lost.
In order to permit changing the value of the symbol, the symbol must
have been originally defined with the SET directive. If the symbol had
been originally defined with QUT or EQU or appeared as an address
label, the value will not change and the R error flag will be posted
to signify a redefinition error.
As with EQU and QUT, any symbols in the expression must have been
defined in a prior source statement; otherwise, the Q error flag
(illegal forward reference) will be posted and the value of the symbol
will remain unchanged.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 84 of 90
20.50. (Symbol) SUB (Expression)
Label: Symbol
Operation: SUB
Operand: An optional expression
Comment: Permitted
Mnemonic definition: SUBroutine entry point.
---
The SUB directive defines the entry point of a subroutine. PAGE8
assembles two contiguous instructions: the first is an indirect JMP
instruction to the next location (which will always be on the same
page as the first instruction). The second location is a data word
that comprises the value of the optional expression. If the expression
is omitted, a default data word of 7402 (octal) is automatically
provided by PAGE8. The default HLT instruction is provided to trap out
any bad jump instructions to the label when the program is first ex-
ecuted.
It is not necessary to define all subroutine entry points with the SUB
directive. However, in order to make use of the RET directive and
allow for automatic paging, it is always desirable to do so. See also
use of the RET directive and the section on SUBROUTINES fur further
description of handling subroutines in PAGE8.
The provision for an optional expression in the SUB directive is made
in order to allow for convenient implementation of coroutines in
PAGE8. A typical coroutine entry is shown in the example below:
COROUT1 SUB Coroutine entry point
COROUT2 SUB 1F Initial linkage at 1H tag
RET COROUT1 Coroutine exit point
1H ... Main-line code of coroutine
...
JMS COROUT2 Call coroutine exit point
... Main-line code continues here
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 85 of 90
20.51. TEXT
Label: Symbol, sequence symbol or blank
Operation: TEXT
Operand: Any text string enclosed in delimiting char-
acters
Comment: Permitted if closing delimiter is present
Mnemonic definition: TEXT string.
----
The TEXT directive generates packed ASCII text strings. The first non-
blank character after the operator should be the delimiter which will
appear at both ends of the string of text. If no terminating delimiter
is found, the text string will be closed out when the end of the line
is found.
The text string is converted so that successive locations are filled
two characters per word with only the low order six bits of the ASCII
character code's being stored. If the string contains an odd number of
characters, the final 6-bit byte will be set to 00 (octal).
If there is not enough room on the current page in an ISEC area, PAGE8
will force a premature page break and store the text string on the
nextg free page. If a full word of zero is needed as a sentinel on the
string, an "at-sign" (@) character can always be used as the final
character of the text string.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 86 of 90
20.52. TITLE (User-defined sub-title)
Label: Sequence symbol or blank
Operation: TITLE
Operand: User-defined text string of 1-60 (decimal)
characters for title
Comment: Treated an an extension of the operand field
Mnemonic definition: TITLE for listing.
-----
The TITLE directive should be followed by a 1-60 (decimal) character
text string which will then become the line 3 title (or sub-title) for
the following pages of the assembly listing. An explicit page eject is
performed before the next statement is listed. If the charfacter
string is longer than 60 (decimal) characters, the remaining char-
acters will be truncated without an error's being noted.
Generally, the second line in any source file should be a TITLE dir-
ective. The TITLE directive should be used frequently in the source
program to aid in the identification of major program segments. As
with the FILE directive, the TITLE directive is not listed so that
both directives can be issued in succession without generating a blank
page between them in the listing. The FILE, TITLE and EJECT directives
do not cause an immediate page eject. They cause a flag to be set
which indicates that a page eject will be needed in front of the next
statement that will actually print on the listing. For example, 8
consecutive EJECT statements have the same effect as a single EJECT
statement.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 87 of 90
20.53. UNLINK (Operation code)
Label: Sequence symbol or blank
Operation: UNLINK
Operand: Any PAGE8 operation code
Comment: Permitted
Mnemonic definition: UNLINK operation code.
------
The UNLINK directive causes the referenced operation code to be rem-
oved from the PAGE8 operation code tables. Subsequent use of that
operation code forces PAGE8 to search the master symbol table in order
to find out if that operation code has been defined as a macro. If
not, the O error flag is posted for an undefined operation code. The
operation code is removed on a temporary basis only and may be "rec-
alled" by the use of the LINK directive.
The primary purpose of this directive is to permit redefinition of
standard PAGE8 operation codes by use of the macro facility. For ex-
ample, when assembling a program for the PDP-8/I that was originally
written for the PDP-8/e, the UNLINK directive could be used to delete
the BSW definition. An appropriate macro could then be defined to
generate in-line code or a subroutine call to emulate the BSW instruc-
tion. This directive can also be used to trap PAGE8 operation codes
for the purpose of providing some special feature (see the description
of the LINK directive for an example). One final use of the UNLINK
directive is to remove operation codes that conflict with the opera-
tion codes of another computer when PAGE8 is being used as a cross-
assembler for that computer.
NOTE: careless use of the UNLINK directive can cause phase errors
during assembly if the directive being unlinked has been used in a
prior source statement. This can occur because PAGE8 does not relink
all unlinked operation codes at the start of each pass. For this
reason, one should be careful to include these LINK and UNLINK dir-
ectives early in the program before any object code has been gen-
erated. The fact that operation codes are not relinked at the start of
each pass can be a useful feature in some special circumstances.
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 88 of 90
21. Alphabetic Listing of all Defined Operation Codes
Legend:
------
mri memory reference.
imri indirect memory reference.
opr operate instruction (7xxx)(octal).
iot I/O instruction (6xxx)(octal).
oasm object code generating assembly directive.
nasm non-object code generating asembly directive.
nasm* assembly directive that causes information to be generated on
the object file, but does not itself cause any information to
be stored at any location within the program.
AFIELD nasm
AGO nasm
AIF nasm
ALIGN nasm
AND mri
ANDI imri
ANDX oasm
ANOP nasm
AREAD nasm
AS oasm
BSW opr
BYTE oasm
CAF iot
CAL opr (CLA CLL)
CAM opr (CLA MQL)
CDF iot
CIA opr (CMA IAC)
CID iot
CIF iot
CLA opr
CLL opr
CMA opr
CML opr
CREF nasm
DC oasm
DCA mri
DCAI imri
DCAX oasm
DI oasm
DSEC nasm
DSI oasm
EJECT nasm
END nasm
EQU nasm
ERM nasm
ERROR: nasm
FIELD nasm*
FILE nasm
FREE nasm
GAP nasm
GTF iot
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 89 of 90
HLT opr
IAC opr
INC mri
INCI imri
INCX oasm
IOF iot
ION iot
IOS iot
IOT iot
ISEC nasm
ISZ mri
ISZI imri
ISZX oasm
JMP mri
JMPI imri
JMPX oasm
JMS mri
JMSI imri
JMSX oasm
LAS opr (CLA OSR)
LDI oasm
LFIELD nasm*
LINK nasm
LIST nasm
LISTC nasm
LISTM nasm
LOAD nasm*
MACRO nasm
MEND nasm
MEXIT nasm
MONR nasm
MQA opr
MQL opr
MSCAN nasm
MSKIP nasm
NOCREF nasm
NOLISTC nasm
NOLISTM nasm
NOP opr
NOTE: nasm
ORG nasm*
OSR opr
PAGE nasm
PART nasm
PUNCH nasm*
QUT nasm
RADIX nasm
RAL opr
RAR opr
RDF iot
RET oasm
RIF iot
RMF iot
ROOM nasm
RTF iot
RTL opr
P A G E 8 -- MACRO ASSEMBLER, V-7B Sep.13, 1993 Page 90 of 90
RTR opr
SET nasm
SKP opr
SMA opr
SNA opr
SNL opr
SPA opr
SRQ iot
STA opr
STL opr
SUB oasm
SWP opr
SZA opr
SZL opr
TAD mri
TADI imri
TADX oasm
TEXT oasm
TITLE nasm
UNLINK nasm