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ST7 Assembler Linker

3 ST7 Assembler

UM0144

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3.6

Conditional assembly

Conditional assembly is used to choose to ignore or select whole areas of assembler code.

This is useful for generating different versions of a program by setting a particular variable in an

INCLUDE

file that forces the use of certain pieces of code instead of others.

3.6.1

#IF, #ELSE and #ENDIF directives

There are three main directives used to perform conditional assembly, as shown in

Table 11.

The condition given with the '#IF' may take the form of any numeric expression. The rule for

deciding whether it resolves to 'true' or 'false' is simple: if it has a zero value then it's false, else

it's true. These directives should NOT start at column 1 of line, reserved for labels. For

example:

#IF {count eq 1}

%OUT 'true'

#ELSE

%OUT 'false'

#ENDIF

This sequence would print 'true' if the label 'count' did equal 1, and ‘false’ if it didn't. For

example:

#IF

{count gt 1}

%OUT count more than one

#IF

{count gt 2}

%OUT ...and more of TWO !

#ELSE

%OUT ...but not more than two!

#ENDIF

#ELSE

%OUT count not more than one

#ENDIF

Table 11.

Summary of assembly directives

Directive

Usage

#IF

marks the start of the conditional and decides whether the following zone will be

assembled or not.

#ELSE

optionally reserves the condition of the previous #IF for the following zone.

#ENDIF

marks the end of the previous #IF's.

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