Comment
Comments are the descriptions of codes. They are used for documentation only and are ignored
by the Cross Assembler. Any text following a semicolon is considered a comment.
Assembly Directives
Directives give direction to the Cross Assembler, specifying the manner in which the Cross Assem
-
bler generates object code at assembly time. Directives can be further classified according to their
behavior as described below.
Conditional Assembly Directives
The conditional block has the following form:
IF
statements
[ELSE
statements]
ENDIF
Syntax
IF expression
IFE expression
·
Description
The directives IF and IFE test the expression following them.
The IF directive grants assembly if the value of the expression is true, i.e. non-zero.
The IFE directive grants assembly if the value of the expression is false, i.e. zero.
· Example
IF debugcase
ACC1 equ 5
extern username: byte
ENDIF
In this example, the value of the variable ACC1 is set to 5 and the username is declared as an
external variable if the symbol debugcase is evaluated as true, i.e. nonzero.
Syntax
IFDEF name
IFNDEF name
·
Description
The directives IFDEF and IFNDEF test whether or not the given name has been defined. The
IFDEF directive grants assembly only if the name is a label, a variable or a symbol. The IFNDEF di
-
rective grants assembly only if the name has not yet been defined. The conditional assembly direc
-
tives support a nesting structure, with a maximum nesting level of 7.
·
Example
IFDEF buf_flag
buffer DB 20 dup(?)
ENDIF
In this example, the buffer is allocated only if the buf_flag has been previously defined.
Chapter 4 Assembly Language and Cross Assembler
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