Table of Contents        Previous topic       Next topic       

CROSS ASSEMBLER->Assembler Macros->Introduction to Assembler Macros

A macro is a powerful tool to enable you to generate multiple lines of code from a single statement.  Coupled with conditional assembly, macros can perform complex tasks.  

There are two aspects to a macro:

- the macro definition
- the macro expansion.

The macro definition does not generate any code.  It simply defines a set of statements for later use during the macro expansion phase.  When the macro is defined it is given a unique name by the user.  The statements included in the macro definition can then be regenerated (expanded) simply by including that name in the operation field of a source code statement (known as a macro call).  Moreover, arguments can be included in the operand field following the macro call.  These arguments are used during expansion to directly replace dummy arguments in the macro definition. Thus a macro can be called many times and different arguments can cause different code to be generated for each call.  The dummy arguments may be in the label, operation or operand fields of the statements in the macro definition and so a very flexible system is possible. The following example illustrates a simple macro definition and macro call. (See sections  and  for descriptions of the directives MACR and ENDM).

Firstly the source code listing:

       TTL     *** Macro Definition and Call ***
       ORG 6000H

var1    ds    1
var2    ds    1

; This is the macro definition:

macxampl MACR  
               LDA \0
               STA \1

; This is the macro call:
               macxampl var1,var2

And now the listing generated during assembly:

   1                            NAM       MACXAMPL
   2                            TTL       *** Macro
                                Definition and Call ***
   3                            LIST
   4                            MEX
   5 6000                       ORG       6000H
   7 6000             var1      ds        1
   8 6001             var2      ds        1
  10                  ; This is the macro definition:
  12                  macxampl MACR
  13                                  LDA \0
  14                                  STA \1
  15                                  ENDM
  17                  ; This is the macro call:
  19                            macxampl  var1,var2
     6002 3A 00 60              LDA       var1
     6005 32 01 60              STA       var2
Assembly complete
Total bytes generated: 8
0 errors
0 warnings

The statements that can be included in a macro definition are:

- executable instructions
- assembler directives
- macro calls

A macro cannot be called until it is has been defined.  The macro definition must therefore precede any reference to it.