.module Directive
Format:
.module string
The .module directive causes the string to be included in the
assemblers output file as an identifier for this particular ob-
ject module. The string may be from 1 to 8 characters in
length. Only one identifier is allowed per assembled module.
The main use of this directive is to allow the linker to report
a modules' use of undefined symbols. At link time all undefined
symbols are reported and the modules referencing them are
listed.
.title Directive
Format:
.title string
The .title directive provides a character string to be placed
on the second line of each page during listing.
.sbttl Directive
Format:
.sbttl string
The .sbttl directive provides a character string to be placed
on the third line of each page during listing.
.page Directive
Format:
.page
The .page directive causes a page ejection with a new heading
to be printed. The new page occurs after the next line of the
source program is processed, this allows an immediately follow-
ing .sbttl directive to appear on the new page. The .page
source line will not appear in the file listing. Paging may be
disabled by invoking the -p directive.
.byte and .db Directives
Format:
.byte exp ;Stores the binary value
.db exp ;of the expression in the
;next byte.
.byte exp1,exp2,expn ;Stores the binary values
.db exp1,exp2,expn ;of the list of expressions
;in successive bytes.
where: exp, represent expressions that will be
exp1, truncated to 8-bits of data.
. Each expression will be calculated
. as a 16-bit word expression,
. the high-order byte will be truncated.
. Multiple expressions must be
expn separated by commas.
The .byte or .db directives are used to generate successive
bytes of binary data in the object module.
.word and .dw Directives
Format:
.word exp ;Stores the binary value
.dw exp ;of the expression in
;the next word.
.word exp1,exp2,expn ;Stores the binary values
.dw exp1,exp2,expn ;of the list of expressions
;in successive words.
where: exp, represent expressions that will occupy two
exp1, bytes of data. Each expression will be
. calculated as a 16-bit word expression.
. Multiple expressions must be
expn separated by commas.
The .word or .dw directives are used to generate successive
words of binary data in the object module.
.blkb, .blkw, and .ds Directives
Format:
.blkb N ;reserve N bytes of space
.blkw N ;reserve N words of space
.ds N ;reserve N bytes of space
The .blkb and .ds directives reserve byte blocks in the ob-
ject module; the .blkw directive reserves word blocks.
.ascii Directive
Format:
.ascii /string/
where: string is a string of printable ascii characters.
/ / represent the delimiting characters. These
delimiters may be any paired printing
characters, as long as the characters are not
contained within the string itself. If the
delimiting characters do not match, the .ascii
directive will give the (q) error.
The .ascii directive places one binary byte of data for each
character in the string into the object module.
.ascis Directive
Format:
.ascis /string/
where: string is a string of printable ascii characters.
/ / represent the delimiting characters. These
delimiters may be any paired printing
characters, as long as the characters are not
contained within the string itself. If the
delimiting characters do not match, the .ascis
directive will give the (q) error.
The .ascis directive places one binary byte of data for each
character in the string into the object module. The last
character in the string will have the high order bit set.
.asciz Directive
Format:
.asciz /string/
where: string is a string of printable ascii characters.
/ / represent the delimiting characters. These
delimiters may be any paired printing
characters, as long as the characters are not
contained within the string itself. If the
delimiting characters do not match, the .asciz
directive will give the (q) error.
The .asciz directive places one binary byte of data for each
character in the string into the object module. Following all
the character data a zero byte is inserted to terminate the
character string.
.radix Directive
Format:
.radix character
where: character represents a single character specifying the
default radix to be used for succeeding numbers.
The character may be any one of the following:
B,b Binary
O,o Octal
Q,q
D,d Decimal
'blank'
H,h Hexidecimal
X,x
.even Directive
Format:
.even
The .even directive ensures that the current location counter
contains an even boundary value by adding 1 if the current loca-
tion is odd.
.odd Directive
Format:
.odd
The .odd directive ensures that the current location counter
contains an odd boundary value by adding one if the current lo-
cation is even.
.area Directive
Format:
.area name [(options)]
where: name represents the symbolic name of the program sec-
tion. This name may be the same as any
user-defined symbol as the area names are in-
dependent of all symbols and labels.
options specify the type of program or data area:
ABS absolute (automatically invokes OVR)
REL relocatable
OVR overlay
CON concatenate
PAG paged area
The .area directive provides a means of defining and separat-
ing multiple programming and data sections. The name is the
area label used by the assembler and the linker to collect code
from various separately assembled modules into one section. The
name may be from 1 to 8 characters in length.
The options are specified within parenthesis and separated by
commas as shown in the following example:
.area TEST (REL,CON) ;This section is relocatable
;and concatenated with other
;sections of this program area.
.area DATA (REL,OVR) ;This section is relocatable
;and overlays other sections
;of this program area.
.area SYS (ABS,OVR) ;(CON not allowed with ABS)
;This section is defined as
;absolute. Absolute sections
;are always overlayed with
;other sections of this program
;area.
.area PAGE (PAG) ;This is a paged section. The
;section must be on a 256 byte
;boundary and its length is
;checked by the linker to be
;no larger than 256 bytes.
;This is useful for direct page
;areas.
The default area type is REL|CON; i.e. a relocatable sec-
tion which is concatenated with other sections of code with the
same area name. The ABS option indicates an absolute area. The
OVR and CON options indicate if program sections of the same
name will overlay each other (start at the same location) or be
concatenated with each other (appended to each other).
Multiple invocations of the .area directive with the same
name must specify the same options or leave the options field
blank, this defaults to the previously specified options for
this program area.
The ASxxxx assemblers automatically provide two program
sections:
'. .ABS.' This dumby section contains all absolute
symbols and their values.
'_CODE' This is the default program/data area.
This program area is of type (REL,CON).
The ASxxxx assemblers also automatically generate two symbols
for each program area:
's_' This is the starting address of the pro-
gram area.
'l_' This is the length of the program area.
.org Directive
Format:
.org exp
where: exp is an absolute expression that becomes the cur-
rent location counter.
The .org directive is valid only in an absolute program section
and will give a (q) error if used in a relocatable program area.
The .org directive specifies that the current location counter
is to become the specified absolute value.
.globl Directive
Format:
.globl sym1,sym2,...,symn
where: sym1, represent legal symbolic names. When
sym2,... When multiple symbols are specified,
symn they are separated by commas.
A .globl directive may also have a label field and/or a com-
ment field.
The .globl directive is provided to define (and thus provide
linkage to) symbols not otherwise defined as global symbols
within a module. In defining global symbols the directive
.globl J is similar to:
J == expression or J::
Because object modules are linked by global symbols, these
symbols are vital to a program. All internal symbols appearing
within a given program must be defined at the end of pass 1 or
they will be considered undefined. The assembly directive (-g)
can be be invoked to make all undefined symbols global at the
end of pass 1.
.if, .else, and .endif Directives
Format:
.if expr
. ;}
. ;} range of true condition
. ;}
.else
. ;}
. ;} range of false condition
. ;}
.endif
The conditional assembly directives allow you to include or
exclude blocks of source code during the assembly process, based
on the evaluation of the condition test.
The range of true condition will be processed if the expres-
sion 'expr' is not zero (i.e. true) and the range of false con-
dition will be processed if the expression 'expr' is zero (i.e
false). The range of true condition is optional as is the .else
directive and the range of false condition. The following are
all valid .if/.else/.endif constructions:
.if A-4 ;evaluate A-4
.byte 1,2 ;insert bytes if A-4 is
.endif ;not zero
.if K+3 ;evaluate K+3
.else
.byte 3,4 ;insert bytes if K+3
.endif ;is zero
.if J&3 ;evaluate J masked by 3
.byte 12 ;insert this byte if J&3
.else ;is not zero
.byte 13 ;insert this byte if J&3
.endif ;is zero
The .if/.else/.endif directives may be nested upto 10 levels.
The .page directive is processed within a false condition
range to allow extended textual information to be incorporated
in the source program with out the need to use the comment
delimiter (;):
.if 0
.page
This text will be bypassed during assembly
but appear in the listing file.
.
.
.
.endif
.include Directive
Format:
.include string
where: string represents a delimited string that is the file
specification of an ASxxxx source file.
The .include directive is used to insert a source file within
the source file currently being assembled. When this directive
is encountered, an implicit .page directive is issued. When the
end of the specified source file is reached, an implicit .page
directive is issued and input continues from the previous source
file. The maximum nesting level of source files specified by a
.include directive is five.
The total number of separately specified .include files is
unlimited as each .include file is opened and then closed during
each pass made by the assembler.
.setdp Directive
Format:
.setdp [base [,area]]
The set direct page directive has a common format in all the
AS68xx assemblers. The .setdp directive is used to inform the
assembler of the current direct page region and the offset ad-
dress within the selected area. The normal invocation methods
are:
.area DIRECT (PAG)
.setdp
or
.setdp 0,DIRECT
for all the 68xx microprocessors (the 6804 has only the paged
ram area). The commands specify that the direct page is in area
DIRECT and its offset address is 0 (the only valid value for all
but the 6809 microprocessor). Be sure to place the DIRECT area
at address 0 during linking. When the base address and area are
not specified, then zero and the current area are the defaults.
If a .setdp directive is not issued the assembler defaults the
direct page to the area "_CODE" at offset 0.
The assembler verifies that any local variable used in a
direct variable reference is located in this area. Local vari-
able and constant value direct access addresses are checked to
be within the address range from 0 to 255.
External direct references are assumed by the assembler to be
in the correct area and have valid offsets. The linker will
check all direct page relocations to verify that they are within
the correct area.
The 6809 microprocessor allows the selection of the direct
page to be on any 256 byte boundary by loading the appropriate
value into the dp register. Typically one would like to select
the page boundary at link time, one method follows:
.area DIRECT (PAG) ; define the direct page
.setdp
.
.
.
.area PROGRAM
.
ldd #DIRECT ; load the direct page register
tfr a,dp ; for access to the direct page
At link time specify the base and global equates to locate the
direct page:
-b DIRECT = 0x1000
-g DIRECT = 0x1000
Both the area address and offset value must be specified (area
and variable names are independent). The linker will verify
that the relocated direct page accesses are within the direct
page.
The preceeding sequence could be repeated for multiple paged
areas, however an alternate method is to define a non-paged area
and use the .setdp directive to specify the offset value:
.area DIRECT ; define non-paged area
.
.
.
.area PROGRAM
.
.setdp 0,DIRECT ; direct page area
ldd #DIRECT ; load the direct page register
tfr a,dp ; for access to the direct page
.
.
.setdp 0x100,DIRECT ; direct page area
ldd #DIRECT+0x100 ; load the direct page register
tfr a,dp ; for access to the direct page
The linker will verify that subsequent direct page references
are in the specified area and offset address range. It is the
programmers responsibility to load the dp register with the cor-
rect page segment corresponding to the .setdp base address
specified.
For those cases where a single piece of code must access a
defined data structure within a direct page and there are many
pages, define a dumby direct page linked at address 0. This
dumby page is used only to define the variable labels. Then
load the dp register with the real base address but donot use a
.setdp directive. This method is equivalent to indexed
addressing, where the dp register is the index register and the
direct addressing is the offset.