4.8.8 Substitution Symbols

Symbols can be assigned a string value. This enables you to create aliases for character strings by equating them to symbolic names. Symbols that represent character strings are called substitution symbols. When the assembler encounters a substitution symbol, its string value is substituted for the symbol name. Unlike symbolic constants, substitution symbols can be redefined.

A string can be assigned to a substitution symbol anywhere within a program; for example:

.asg "AR1", myReg ;register AR1 .asg "*+XAR2 [2]", ARG1 ;first arg .asg "*+XAR2 [1]", ARG2 ;second arg

When you are using macros, substitution symbols are important because macro parameters are actually substitution symbols that are assigned a macro argument. The following code shows how substitution symbols are used in macros:

add2 .macro A, B ; add2 macro definition MOV AL, A ADD AL, B .endm *add2 invocation add2 LOC1, LOC2 ;add "LOC1" argument to a ;second argument "LOC2". MOV AL,LOC1 ADD AL,LOC2

See Section 6 for more information about macros.