Online HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens
Macro Assembler Directives
Processor Code Generation Directives
.186 enables assembly of 80186 instructions
.286 enables assembly of non privileged 80286 instructions
.286C same as .286
.286P enables assembly of all 80286 instructions
.287 enabled assembly of 80287 instructions
.386 enabled assembly of non privileged 80386 instructions
If used before .MODEL segments are defined as 32bits.
Causes all segments to default to DWORD alignment.
.386P enabled assembly of all 80386 instructions (see .386)
.387 enabled assembly of 80387 instructions
.8086 default, enables assembly of 8088/8086 instruction
.8087 default, enables assembly of 8087 instructions
These directives must precede the segment they are to effect.
they cannot occur within a segment.
Memory Model Directives
.CODE [name] starts code segment; must follow .MODEL directive
.CONST starts a constant data segment with name CONST;
must follow .MODEL directive; placed in DGROUP
.DATA starts a near data segment for initialized data
with name _DATA; must follow .MODEL directive;
placed in DGROUP
.DATA? starts a near data segment for uninitialized
data with name _BSS; must follow .MODEL
directive; placed in DGROUP
.FARDATA [name] not placed in any group
.FARDATA? [name] not placed in any group
.MODEL model defines memory model to be one of the following:
SMALL, COMPACT, MEDIUM, LARGE or HUGE; must be
used prior to any other segment directive
.STACK [size] indicates start of stack segment named 'STACK'
with size indicating number of bytes to reserve,
default is 1k; placed in DGROUP
Segment Definition, Segment Ordering and Linkage Directives
.ALPHA orders segments alphabetically
.SEQ orders segments sequentially (default)
ASSUME sreg:name [,sreg:name...] selects default segment
register to be used by the assembler, not the CPU,
for addressing all symbols in the segment or group.
Name must be associated with a SEGMENT or GROUP
or set to "NOTHING" to indicate no segment register
is to be associated.
COMM def [,def...] defines variables that are both public and
external (communal). Can be used in and include
file to identify it to each source file without
declaring it in each model as extern. Actually
defines data once. Communal variables cannot be
initialized, and are not guaranteed to be allocated
contiguously since these are allocated by the linker.
DOSSEG orders segments the same as DOS. This is Microsoft
languages default order; causes paragph alignment
END [name] marks end of source module and sets program
start address (CS:IP) if 'name' is present
name ENDP ends procedure 'name'
name ENDS ends a segment or structure
EXTRN name:type [,name:type...] defines one or more external symbols
name GROUP seg[,seg]
name LABEL [NEAR|FAR|PROC] defines an entry point; If PROC is specified,
it's value depends on the current MODEL
NAME pgmName ignored since MASM 5.0; used to set module name
name PROC [NEAR|FAR] defines procedure; NEAR/FAR has .MODEL default
PUBLIC name[,name...] makes symbol 'name' available to other modules
name SEGMENT [align][combine][use]['class']
align = BYTE align on byte address (no alignment)
= WORD align on even address
= DWORD align on DWORD address
= PARA align on next 16 byte paragraph
= PAGE align on next 256 byte boundary
combine = PUBLIC similar named segments are concatenated (CS)
= STACK similar named segments are concatenated (SS)
= COMMON similar named segment are overlapped
= MEMORY similar names segments are concatenated
= AT addr segment relative to absolute address
= nothing segment is private and loaded independent
use = USE16 segments will be 16 bits (if .386)
= USE32 segments will be 32 bits (if .386)
Data Allocation Directives
ALIGN n aligns next variable or instruction on a boundary
that is a multiple of "n". This can speed memory
fetches on 16 and 32 bit CPU'S if aligned. New to
MASM 5.0, previous versions used EVEN. Can result
in NOP's added to code.
[name] DB init[,init...] define byte
[name] DD init[,init...] define double word (DWORD, 4 bytes)
[name] DF init[,init...] define far word (FWORD, 386, 6 bytes)
[name] DQ init[,init...] define quad word (QWORD, 8 bytes)
[name] DT init[,init...] define temp word (TBYTE, 10 bytes)
[name] DW init[,init...] define word (WORD, 2 bytes)
count DUP (init[,init...]) duplicate 'init' 'count' times; DUP can be
nested to 17 levels; DUP'ed initial values
of (?) don't result in data in the object file
but instead increment the next data addr
name ENDS end of structure or segment
EVEN same as align 2; Aligns data on even boundary
ORG expr sets location counter to 'expr'; If 'expr'
is '$' the code is ORG'ed at the current loc.
name RECORD fld[,fld...] defines a byte or word variable
consisting of bit fields; fields have the format:
fieldname:width[=expr]; the sum of all widths
must be <= 0
[name] STRUC <[init[,init]]> defines beginning of a structure; Values
between <> are initializers; The '<>' symbols
are required.
Logical and Bit Oriented Directives
expr1 AND expr2 returns nonzero if any set bit matches
expr1 EQ expr2 returns (-1) for true or (0) for false
expr1 GE expr2 returns (-1) for true or (0) for false
expr1 LE expr2 returns (-1) for true or (0) for false
expr1 LT expr2 returns (-1) for true or (0) for false
MASK {fldname|record} returns bit mask for bits in record
expr1 OR expr2 returns bitwise OR on expr1 and expr2
NOT expr returns 'expr' with all bits reversed
expr SHL count returns expr shifted left count times
expr SHR count returns expr shifted right count times
WIDTH {fldname|record} returns width of field in bit record
expr1 XOR expr2 returns bitwise XOR on expr1 and expr2
Other Operators and Directives
[] index operator, same as addition
.MSFLOAT encode floats in Microsoft Real Format
.TYPE expr returns byte defining mode and scope of expr
name EQU expr assigns expression to name. surround text with <>
HIGH expr returns high byte of 'expr'
INCLUDE filespec inserts code from 'filespec' into file
INCLUDELIB filespec stores link library info in .OBJ file
LENGTH var returns number of data objects in DUPed 'var'
LOW expr returns low byte of 'expr'
expr1 MOD expr2 return remainder of expr1/expr2
OFFSET expr returns offset of expr; When .MODEL is used
the offset of a group relative segment refers
to the end of the segment
type PTR expr forces 'expr' to 'type'
SEG expr returns segment of expression
SHORT sets type of label to short, less than 128
bytes from start of next instruction
SIZE var returns # of bytes allocated by DUP directive
THIS type returns an operand of specified type whose
offset and segment values are equal to the
current location
TYPE expr returns type of expression
Program Listing and Documentation Directives
.CREF restores listing of cross reference symbols
.LALL include macro expansion in listings
.LFCOND include false conditional blocks in listings
.LIST starts listing of statements
.SALL suppress listing of all macro expansions
.SFCOND suppress false conditional blocks in listings
.XALL start listing of macro expansion
.XCREF [name[,name...]] suppress symbols in cross reference
.XLIST suppress program listing
COMMENT delimiter [text]
PAGE [[len],wid] sets page length&width or ejects if no parms
SUBTTL text defines program listing subtitle
TITLE text defines program listing title
Condition Assembly Directives
ELSE else clause for conditional assembly block
ENDIF terminates a conditional assembly block
IFDEF name conditional assembly if name is defined
Macro Definition Directives
ENDM terminates a macro block
EXITM exit macro expansion immediately
IRP parm,<arg[,arg...]> parm in the statements enclosed by the
IRP and ENDM will be repeated and replaced with the
values of "arg" for each "arg" in the <>.
IRPC parm,<string> parm in the statements enclosed by the IRPC
and ENDM will be repeated and replaced with the values
of each char in the "string" for each character
position in the string. "string" should be enclosed
in <> if it contains spaces or other separators.
LOCAL name[,name...] defines scope symbol as local to a macro
name MACRO [parm[,parm...]] defines a macro and it's parameters
PURGE name[,name] purges macros from memory
REPT expr repeats all statements through ENDM statement for
'expr' times
User Message Directives
.ERR generates and error
.ERR1 generates an error on PASS 1
.ERR2 generates an error on PASS 2
.ERRB <arg> generates an error if 'arg' is blank
.ERRDEF name generates an error if 'name' is previously defined
.ERRDIF[I] <arg1>,<arg2>
.ERRE expr generates and error is 'expr' is false
%OUT text displays 'text' to console
Predefined Equates (available only if simplified segments are used)
@curseg contains the current segment
@filename current file name without extension
@code contains the current code segment
@codesize 0 for small & compact, 1 for large, medium & huge
@datasize 0 for small & medium, 1 for compact & large, 2=huge
@const contains segment of define by .CONST
@data contains segment of define by .DATA
@data? contains segment of define by .DATA?
@fardata contains segment of define by .FARDATA
@fardata? contains segment of define by .FARDATA?
@stack contains segment of define by .STACK
Most of these are only available if the simplified segment system
is used. @curseg and @filename are available regardless.
Radix Specifiers
.RADIX expr sets radix [2..16] for numbers (dec. default)
B binary data specifier
Q octal data specifier
O octal data specifier
D decimal data specifier
H hexadecimal data specifier
[helppc.bosbyte.nl] asm directives