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7 The SASM Assembler

Page 54

• SX-Key/Blitz Development System Manual 2.0 • Parallax, Inc.

The following example demonstrates the use of the IF...ELSE directive.

Delay

EQU

Choice

EQU

Delay >=9

mov

$08, #5

add

$09, #%011

ENDIF

Choice = 0

mov

$0A, #$1B

ELSE

mov

$0A, #$1C

ENDIF

The condition for an IF...ELSE directive can contain expressions and multiple conditional statements.

Two or more conditional statements may be specified by appending them together with the conditional

operators NOT, AND, OR and XOR. For example:

IF choice = 1 AND delay > 9

would assemble the code block following it if choice equals 1 and delay is greater than 9 at assemble time.

If the statement or expression evaluates to anything other than zero (0), the condition is true; otherwise,

the condition is false.

7.3.13 The IF{N}DEF…ELSE…ENDIF Directives

The IFDEF…ELSE (if defined) and IFNDEF…ELSE (if not defined) directives are very similar to the

IF…ELSE directive. The difference is they assemble or prevent assembly of code blocks based on

whether a symbol is defined or not. For example:

DriverOn

EQU 1

IFDEF

DriverOn

{some code block here}

ENDIF

would assemble the code block in the IFDEF statement because the DriverOn symbol was defined. If

DriverOn

was not defined (i.e. line number 1, above, was commented out) the code block would be ig-

nored.

Note that SASM considers labels to be defined when there is an assignment using EQU or “=” in the

code before the IF{N}DEF directive, whereas the Parallax Assembler only accepts assignments using

EQU.

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