## The Assembler Description

### ... General Assembler Directives

####

       An  ASxxxx  directive  is placed in the operator field of the
    source line.  Only one directive is  allowed  per  source  line.
    Each  directive  may  have  a blank operand field or one or more
    operands.  Legal operands differ with each directive.

####

- .module Directive
- .title Directive
- .sbttl Directive
- .page Directive
- .msg Directive
- .error Directive
- .byte, .db, and .fcb Directives
- .word, .dw, and .fdb Directives
- .3byte and .triple Directives
- .4byte and .quad Directives
- .blkb, .ds, .rmb, and .rs Directives
- .blkw, .blk3, and .blk4 Directives
- .ascii, .fcc, and .str Directives
- .ascis and .strs Directives
- .asciz and .strz Directives
- .assume Directive
- .radix Directive
- .even Directive
- .odd Directive
- .area Directive
- .bank Directive
- .org Directive
- .globl Directive
- .local Directive
- .equ, .gblequ, and .lclequ Directives
- .if, .else, and .endif Directives
- .ifxx, .else, and .endif Directives
- .ifdef, .else, and .endif Directives
- .ifndef, .else, and .endif Directives
- .include Directive
- .define and .undefine Directives
- .setdp Directive
- .16bit, .24bit, and .32bit Directives
- .msb Directive
- .end Directive
- Return to the Assembler Index

####

    .module Directive

    Format:

            .module name

       The  .module  directive causes the name to be included in the
    assemblers output file as an identifier for this particular  ob-
    ject module.  The name may be from 1 to 79 characters in length.
    The name may not have any embedded white space (spaces or tabs).
    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.

##### => Section Index

####

    .title Directive

    Format:

            .title  string

       The .title directive provides a character string to be placed
    on the second line of each page during listing.  The string  be-
    gins  with  the first non white space character (after any space
    or tab) and ends with the end of the line.

##### => Section Index

####

    .sbttl Directive

    Format:

            .sbttl  string

       The .sbttl directive provides a character string to be placed
    on the third line of each page during listing.  The  string  be-
    gins  with  the first non white space character (after any space
    or tab) and ends with the end of the line.

##### => Section Index

####

    .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.

##### => Section Index

####

    .error Directive

    Format:

            .msg /string/

    where:  string  represents a text string.  The string is printed
                    to the console during the final assembly pass.

            /  /    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 .msg
                    directive will give the (q) error.

       The  .msg  directive  is  useful to report assembly status or
    other information during the assembly process.

##### => Section Index

####

    .error Directive

    Format:

            .error exp

    where:  exp     represents   an  absolute  expression.   If  the
                    evaluation of the expression results  in  a  non
                    zero value then an 'e' error is reported and the
                    text line is listed in the generated error.

       The  .error  directive  is  useful to report configuration or
    value errors during the assembly process.  (The .error directive
    is  identical in function to the .assume directive, just perhaps
    more descriptive.)

##### => Section Index

####

    .byte, .db, and .fcb Directives

    Format:

            .byte   exp             ;Stores the binary value
            .db     exp             ;of the expression in the
            .fcb    exp             ;next byte.

            .byte   exp1,exp2,expn  ;Stores the binary values
            .db     exp1,exp2,expn  ;of the list of expressions
            .fcb    exp1,exp2,expn  ;in successive bytes.

    where:  exp,    represent expressions that will be
            exp1,   truncated to 8-bits of data.
            .       Each expression will be calculated,
            .       the high-order byte will be truncated.
            .       Multiple expressions must be
            expn    separated by commas.

       The  .byte, .db, or .fcb directives are used to generate suc-
    cessive bytes of binary data in the object module.

##### => Section Index

####

    .word, .dw, and .fdb Directives

    Format:

            .word   exp             ;Stores the binary value
            .dw     exp             ;of the expression in
            .fdb    exp             ;the next word.

            .word   exp1,exp2,expn  ;Stores the binary values
            .dw     exp1,exp2,expn  ;of the list of expressions
            .fdb    exp1,exp2,expn  ;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, .dw, or .fdb directives are used to generate suc-
    cessive words of binary data in the object module.

##### => Section Index

####

    .3byte and .triple Directive

    Format:

            .3byte  exp             ;Stores the binary value
            .triple exp             ;of the expression in
                                    ;the next triple (3 bytes).

            .3byte  exp1,exp2,expn  ;Stores the binary values
            .triple exp1,exp2,expn  ;of the list of expressions
                                    ;in successive triples
                                    ;(3 bytes).

    where:  exp,    represent expressions that will occupy three
            exp1,   bytes of data. Each expression will be
            .       calculated as a 24-bit word expression.
            .       Multiple expressions must be
            expn    separated by commas.

       The  .3byte  or .triple directive is used to generate succes-
    sive triples of binary data in the object module.  (These direc-
    tives   are  only  available  in  assemblers  supporting  24-bit
    addressing.)

##### => Section Index

####

    .4byte and .quad Directives

    Format:

            .4byte  exp             ;Stores the binary value
            .quad   exp             ;of the expression in
                                    ;the next quad (4 bytes).

            .4byte  exp1,exp2,expn  ;Stores the binary values
            .quad   exp1,exp2,expn  ;of the list of expressions
                                    ;in successive quads
                                    ;(4 bytes).

    where:  exp,    represent expressions that will occupy three
            exp1,   bytes of data. Each expression will be
            .       calculated as a 32-bit word expression.
            .       Multiple expressions must be
            expn    separated by commas.

       The  .4byte or .quad directive is used to generate successive
    quads of binary data in the object module.  (This  directive  is
    only available in assemblers supporting 32-bit addressing.)

##### => Section Index

####

    .blkb, .ds, .rmb, and .rs Directives

    Format:

            .blkb   N       ;reserve N bytes of space
            .ds     N       ;reserve N bytes of space
            .rmb    N       ;reserve N bytes of space
            .rs     N       ;reserve N bytes of space

       The  .blkb, .ds, .rmb, and .rs directives reserve byte blocks
    in the object module;

##### => Section Index

####

    .blkw, .blk3, and .blk4 Directives

    Format:

            .blkw   N       ;reserve N words of space
            .blk3   N       ;reserve N triples of space
            .blk4   N       ;reserve N quads of space

       The .blkw directive reserves word blocks;  the .blk3 reserves
    3  byte  blocks(available  in   assemblers   supporting   24-bit
    addressing);  the .blk4 reserves 4 byte blocks (available in as-
    semblers supporting 32-bit addressing).

##### => Section Index

####

    .ascii, .fcc and .str Directives

    Format:

            .ascii  /string/

            .fcc    /string/

            .str    /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,  .fcc, and .str directives place one binary byte of
    data for each character in the string into the object module.

##### => Section Index

####

    .ascis and .strs Directives

    Format:

            .ascis  /string/

            .strs   /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
                    and .strs directives will give the (q) error.

       The .ascis and .strs directives place 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.

##### => Section Index

####

    .asciz and .strz Directives

    Format:

            .asciz  /string/

            .strz   /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
                    and .strz directive will give the (q) error.

       The .asciz and .strz directives place one binary byte of data
    for each character in the string into the object  module.   Fol-
    lowing  all  the  character data a zero byte is inserted to ter-
    minate the character string.

##### => Section Index

####

    .assume Directive

    Format:

            .assume exp

    where:  exp     represents   an  absolute  expression.   If  the
                    evaluation of the expression results  in  a  non
                    zero value then an 'e' error is reported and the
                    text line is listed in the generated error.

       The  .assume  directive  is useful to check assumptions about
    assembler values.  (The .assume directive is identical in  func-
    tion to the .error directive, just perhaps more descriptive.)

##### => Section Index

####

    .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

##### => Section Index

####

    .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.

##### => Section Index

####

    .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.

##### => Section Index

####

    .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  or  bank as the area names
                    are independent  of  all  symbols,  labels,  and
                    banks.

            options specify the type of program or data area:
                    ABS     absolute (automatically invokes OVR)
                    REL     relocatable
                    OVR     overlay
                    CON     concatenate
                    NOPAG   non-paged area
                    PAG     paged area

            options specify a code or data segment:
                    CSEG    Code segment
                    DSEG    Data segment

            option  specifies the data area bank:
                    BANK    Named collection of areas

       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 79 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).

       The  area can be specified as either a code segment, CSEG, or
    a data segment, DSEG.  The CSEG and DSEG descriptors are  useful
    when  the  microprocessor  code  and  data  unit allocations are
    unequal:  e.g.  the executable code  uses  an  allocation  of  2
    bytes for each instruction and is addressed at an increment of 1
    for every instruction, and the data uses an allocation of 1 byte
    for  each element and is addressed at an increment of 1 for each
    data byte.  The allocation units are defined by the architecture
    of the particular microprocessor.

       The  .area  directive also provides a means of specifying the
    bank this area is associated with.  All areas associated with  a
    particular  bank  are  combined  at  link  time  into a block of
    code/data.

       The  CSEG,  DSEG,  and  BANK options are specified within the
    parenthesis as shown in the following examples:

            .area   C_SEG   (CSEG,BANK=C1)
                                    ;This is a code section
                                    ;and is included in bank C1
            .area   D_SEG   (DSEG,BANK=D1)
                                    ;This is a data section
                                    ;and is included in bank D1.

       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:

            '_CODE'         This  is  the  default  code/data  area.
                            This   program   area   is    of    type
                            (REL,CON,CSEG).

            '_DATA'         This  is the default optional data area.
                            This   program   area   is    of    type
                            (REL,CON,DSEG).

    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.

    The .area names and options are never case sensitive.

##### => Section Index

####

    .bank Directive

    Format:

            .bank   name    [(options)]

    where:  name    represents  the  symbolic  name of the bank sec-
                    tion.   This  name  may  be  the  same  as   any
                    user-defined  symbol  or  area as the bank names
                    are independent  of  all  symbols,  labels,  and
                    areas.   The name may be from 1 to 79 characters
                    in length.

            options specify the parameters of the bank:
                    BASE    base address of bank
                    SIZE    maximum size of bank
                    FSFX    file suffix for this bank
                    MAP     NOICE mapping

       The  .bank  directive allows an arbitrary grouping of program
    and/or data areas to be communicated to the  linker.   The  bank
    parameters are all optional and are described as follows:

         1.  BASE, the  starting  address of the bank (default is 0)
             may be defined.  This address can be overridden by  us-
             ing  the linker -b option for the first area within the
             bank.  The bank address is always specified  in  'byte'
             addressing.  A first area which is not 'byte' addressed
             (e.g.  a processor addressed by a 'word' of 2  or  more
             bytes)  has  the  area  address  scaled to begin at the
             'byte' address.

         2.  SIZE, the  maximum  length  of  the  bank  specified in
             bytes.  The size is always specified in terms of bytes.

         3.  FSFX, the file suffix to be used by the linker for this
             bank.  The suffix may not contain embedded white space.

         4.  MAP,  NOICE   mapping   parameter   for  this  bank  of
             code/data.

       The options are specified within parenthesis and separated by
    commas as shown in the following example:

            .BANK  C1  (BASE=0x0100,SIZE=0x1000,FSFX=_C1)
                                    ;This bank starts at 0x0100,
                                    ;has a maximum size of 0x1000,
                                    ;and is to be placed into
                                    ;a file with a suffix of _C1

               The parameters must be absolute (external symbols are not al-
            lowed.)

##### => Section Index

####

    .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.

##### => Section Index

####

    .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.

       Naming  a  symbol  not  existing in the current assembly in a
    .globl directive will cause a 'u' error.

       The  .globl directive and == construct can be overridden by a
    following .local directive.

                                  NOTE

         The  ASxxxx  assemblers  use the last occurring symbol
         specification in the source file(s) as the type  shown
         in the symbol table and output to the .rel file.

##### => Section Index

####

    .local Directive

    Format:

            .local  sym1,sym2,...,symn

    where:  sym1,           represent legal symbolic names.
            sym2,...        When multiple symbols are specified,
            symn            they are separated by commas.

       A  .local directive may also have a label field and/or a com-
    ment field.

       The  .local  directive is provided to define symbols that are
    local to the current assembly process.  Local  symbols  are  not
    effected  by  the assembler option -a (make all symbols global).
    In defining local symbols the directive .local J is similar to:

          J =: expression

       The  .local directive and the =:  construct are useful in de-
    fining symbols and constants within a header or definition  file
    that contains many symbols specific to the current assembly pro-
    cess that should not be exported into the .rel output  file.   A
    typical  usage  is  in  the definition of SFRs (Special Function
    Registers) for a microprocessor.

       The .local directive and =:  construct can be overridden by a
    following .globl directive.

       A  defined  symbol  that  has  not been given a value is con-
    sidered an external variable and will cause an 'r'  error  in  a
    .local  directive  and  its symbol type will not be changed.  An
    undefined symbol in a .local directive causes a 'u' error.

                                  NOTE

         The  ASxxxx  assemblers  use the last occurring symbol
         specification in the source file(s) as the type  shown
         in the symbol table and output to the .rel file.

##### => Section Index

####

    .equ, .gblequ, and .lclequ Directives

    Format:

            sym1    .equ    expr    ; equivalent to sym1  = expr
            sym2    .gblequ expr    ; equivalent to sym2 == expr
            sym3    .lclequ expr    ; equivalent to sym3 =: expr

       These  alternate  forms  of equivalence are provided for user
    convenience.

##### => Section Index

####

    .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

##### => Section Index

####

    .ifxx, .else, and .endif Directives
       Additional  conditional  directives are available to test the
    value of an evaluated expression:

            .ifne   expr            ; true if expr != 0
            .ifeq   expr            ; true if expr == 0
            .ifgt   expr            ; true if expr >  0
            .iflt   expr            ; true if expr <  0
            .ifge   expr            ; true if expr >= 0
            .ifle   expr            ; true if expr <= 0

       Format:

            .ifxx   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 test condition.

       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:

            .ifne   A-4             ;evaluate A-4
            .byte   1,2             ;insert bytes if A-4 is
            .endif                  ;not zero

            .ifeq   K+3             ;evaluate K+3
            .byte   3,4             ;insert bytes if K+3
            .endif                  ;is zero

            .ifne   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 .ifxx/.else/.endif directives may be nested upto 10 levels.

##### => Section Index

####

    .ifdef, .else, and .endif Directives

    Format:

            .ifdef  sym
            .                       ;}
            .                       ;} 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 symbol
    'sym' has been defined with a .define directive or  'sym'  is  a
    variable  with  an  assigned  value else the false range will be
    processed.  The range of true condition is optional  as  is  the
    .else directive and the range of false condition.  The following
    are all valid .ifdef/.else/.endif constructions:

            .ifdef  sym$1           ;lookup symbol sym$1
            .byte   1,2             ;insert bytes if sym$1 is
            .endif                  ;defined

            .ifdef  sym$2           ;lookup symbol sym$2
            .else
            .byte   3,4             ;insert bytes if sym$1
            .endif                  ;is not defined

            .ifdef  sym$3           ;lookup symbol sym$3
            .byte   12              ;insert this byte if sym$3
            .else                   ;is defined
            .byte   13              ;insert this byte if sym$3
            .endif                  ;is not defined

    The .ifdef/.else/.endif directives may be nested upto 10 levels.

##### => Section Index

####

    .ifndef, .else, and .endif Directives

    Format:

            .ifndef sym
            .                       ;}
            .                       ;} 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 symbol
    'sym' is not defined by a .define directive and a variable 'sym'
    has  not been assigned a value else the range of false condition
    will be processed.  The range of true condition is  optional  as
    is  the  .else  directive and the range of false condition.  The
    following are all valid .ifndef/.else/.endif constructions:

            .ifndef sym$1           ;lookup symbol sym$1
            .byte   1,2             ;insert bytes if sym$1 is
            .endif                  ;not defined

            .ifndef sym$2           ;lookup symbol sym$2
            .else
            .byte   3,4             ;insert bytes if sym$1
            .endif                  ;is defined

            .ifndef sym$3           ;lookup symbol sym$3
            .byte   12              ;insert this byte if sym$3
            .else                   ;is not defined
            .byte   13              ;insert this byte if sym$3
            .endif                  ;is defined

    The  .ifndef/.else/.endif  directives may be nested upto 10 lev-
    els.

##### => Section Index

####

    .include Directive

    Format:

            .include        /string/

    where:  string  represents  a string that is the file specifica-
                    tion of an ASxxxx source file.

            /  /    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 .include
                    directive will give the (q) error.

       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.

       The  default  directory  path,  if none is specified, for any
    .include file is the directory path of the  current  file.   For
    example:   if  the  current  source file, D:\proj\file1.asm, in-
    cludes  a  file  specified   as   "include1"   then   the   file
    D:\proj\include1.asm is opened.

##### => Section Index

####

    .define and .undefine Directives

    Format:

            .define        keyword  /string/

            .undefine      keyword

    where:  keyword is  the  substitutable  string  which must start
                    with a letter and may contain any combination of
                    digits and letters.

    where:  string  represents  a string that is substituted for the
                    keyword.  The string may contain any sequence of
                    characters including white space.

            /  /    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 .define
                    directive will give the (q) error.

       The  .define  directive specifies a user defined string which
    is substituted for the keyword.  The substitution string may it-
    self  contain other keywords that are substitutable.  The assem-
    bler resumes the parse of the line at the point the keyword  was
    found.  Care must be excersized to avoid any circular references
    within .define directives, otherwise the assembler may  enter  a
    'recursion runaway' resulting in an 's' error.

       The  .undefine  directive removes the keyword as a substitut-
    able string.  No error is returned if the keyword  was  not  de-
    fined.

##### => Section Index

####

    .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.

##### => Section Index

####

    .16bit, .24bit, and .32bit Directives

    Format:

            .16bit          ;specify 16-bit addressing
            .24bit          ;specify 24-bit addressing
            .32bit          ;specify 32-bit addressing

       The  .16bit, .24bit, and .32bit directives are special direc-
    tives for assembler configuration when default  values  are  not
    used.

##### => Section Index

####

    .msb Directive

    Format:

            .msb    n

       The  .msb  directive is only available in selected assemblers
    which support 24- or 32-bit addressing.

       The  assembler operator '>' selects the upper byte (MSB) when
    included in an assembler instruction.  The default assembler mode
    is  to select bits <15:8> as the MSB.  The .msb directive allows
    the programmer to specify a particular byte as  the  'MSB'  when
    the address space is larger than 16-bits.

       The  assembler  directive  .msb n  configures the assembler to
    select a particular byte as MSB.  Given a 32-bit address of MNmn
    (M(3)  is  <31:24>, N(2) is <23:16>, m(1) is <15:8>, and n(0) is
    <7:0>) the following examples show how to  select  a  particular
    address byte:

            .msb 1          ;select byte 1 of address
                            ;<M(3):N(2):m(1):n(0)>
            LD A,>MNmn      ;byte m <15:8> ==>> A
            ...

            .msb 2          ;select byte 2 of address
                            ;<M(3):N(2):m(1):n(0)>
            LD A,>MNmn      ;byte N <23:16> ==>> A
            ...

            .msb 3          ;select byte 3 of address
                            ;<M(3):N(2):m(1):n(0)>
            LD A,>MNmn      ;byte M <31:24> ==>> A
            ...

##### => Section Index

####

    .end Directive

    Format:

            .end

            .end    exp

    where:  exp     represents  any expression, including constants,
                    symbols, or labels.

       The  .end  directive is used to specify a code entry point to
    be included in the linker output file.  Review  the  I86  and  S
    record formats described in the linker section for details.

       The .end directive without an expression is ignored.

##### => Section Index

####

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Last Updated: January 2006