SLAU131Y October 2004 – June 2021
If you want to call a macro several times with different data each time, you can assign parameters within the macro. The macro language supports a special symbol, called a substitution symbol, which is used for macro parameters.
Macro parameters are substitution symbols that represent a character string. These symbols can also be used outside of macros to equate a character string to a symbol name (see Section 5.9.9).
Valid substitution symbols can be up to 128 characters long and must begin with a letter. The remainder of the symbol can be a combination of alphanumeric characters, underscores, and dollar signs.
Substitution symbols used as macro parameters are local to the macro they are defined in. You can define up to 32 local substitution symbols (including substitution symbols defined with the .var directive) per macro. For more information about the .var directive, see Section 7.4.6.
During macro expansion, the assembler passes arguments by variable to the macro parameters. The character-string equivalent of each argument is assigned to the corresponding parameter. Parameters without corresponding arguments are set to the null string. If the number of arguments exceeds the number of parameters, the last parameter is assigned the character-string equivalent of all remaining arguments.
If you pass a list of arguments to one parameter or if you pass a comma or semicolon to a parameter, you must surround these terms with quotation marks.
At assembly time, the assembler replaces the macro parameter/substitution symbol with its corresponding character string, then translates the source code into object code.
The following example shows the expansion of a macro with varying numbers of arguments.
Macro definition:
Parms.macro a,b,c
; a = :a:
; b = :b:
; c = :c:
.endmCalling the macro:
Parms 100,label Parms 100,label,x,y
; a = 100 ; a = 100
; b = label ; b = label
; c = "" ; c = x,y
Parms 100, , x Parms "100,200,300",x,y
; a = 100 ; a = 100,200,300
; b = "" ; b = x
; c = x ; c = y
Parms """string""",x,y
; a = "string"
; b = x
; c = y