This chapter introduces the basic macro concept: what you can use the macro facility for, how you can prepare your own macro definitions, and how you call these macro definitions for processing by the assembler.

Macro language is an extension of assembler language. It provides a convenient way to generate a sequence of assembler language statements many times in one or more programs. A macro definition is written only once; thereafter, a single statement, a macro instruction statement, is written each time you want to generate the sequence of statements. This simplifies the coding of programs, reduces the chance of programming errors, and ensures that standard sequences of statements are used to accomplish the functions you want.

In addition, conditional assembly lets you code statements that are assembled or not, depending upon conditions evaluated at conditional assembly time. These conditions are generally tests of values which can be defined, set, changed, and tested during assembly. Conditional assembly statements can be used within macro definitions or in open code.