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UM0144

For example:

This macro creates the code for a loop to await IO port at $C000 to go low. Without the LOCAL

directive, the label 'loop' would be defined as many times as the macro is called, producing

syntax errors at assembly time.

Because it's been declared LOCAL at the start of the MACRO definition, the assembler takes

care of it. Wherever it sees the label 'loop' inside the macro, it changes the name 'loop' to

'LOCXXXX' where XXXX is a hex number from 0000 to FFFF.

Each time a local label is used, XXXX is incremented. So, the first time the getio macro is

called, 'loop' is actually defined as 'LOC0', the second time as 'LOC1' and so on, each of these

being a unique reference name. The reference to 'loop' in the 'if' statement is also detected

and changed to the appropriate new local variable.

The directives in

Table 10 are very useful, in conjunction with macros:

3.5.2

Parameter substitution

The assembler looks for macro parameters after every space character. If you want to embed a

parameter, for example, in the middle of a label, you must precede the parameter name with an

ampersand '&' character, to make the parameter visible to the preprocessor. For example, if we

have a parameter called 'param'.,

dc.w param

it works as expected, but the ampersand is necessary on:

label&param:nop

label&param&_&param:nop

Otherwise 'labelparam' would be left as a valid label name; If the macro parameter 'param'

had the value '5', then 'label5' and 'label5_5' would be created.

getio

MACRO

LOCAL loop

loop

ld A,$C000

jra loop

MEND

Table 10.

Some useful directives

Directive

Usage

#IFB

To implement macro optional parameters.

#IFDEF

To test if a parameter is defined.

#IFLAB

To test if a parameter is a label.

#IFIDN

To compare a parameter to a given string.

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