Zilog ZUSBOPTS - Manual (Page 279)

UM017105-0511 Labels
Zilog Developer Studio II – ZNEO™
User Manual
251
Anonymous Labels
The ZDS II assembler supports anonymous labels. Table 22 lists the reserved symbols pro-
vided for this purpose.
Local Labels
Any label beginning with a dollar sign ( $ ) or ending with a question mark ( ? ) is consid-
ered to be a local label. The scope of a local label ends when a SCOPE directive is encoun-
tered, thus allowing the label name to be reused. A local label cannot be imported or
exported.
Example
$LOOP: JP $LOOP ; Infinite branch to $LOOP
LAB?: JP LAB? ; Infinite branch to LAB?
SCOPE ; New local label scope
$LOOP: JP $LOOP ; Reuse $LOOP
LAB?: JP LAB? ; Reuse LAB?
Importing and Exporting Labels
Labels can be imported from other modules using the EXTERN or XREF directive. A space
can be provided in the directive to indicate the label’s location. Otherwise, the space of the
current segment is used as the location of the label.
Labels can be exported to other modules by use of the PUBLIC or XDEF directive.
Label Spaces
The assembler makes use of a label’s space when checking the validity of instruction oper-
ands. Certain instruction operands require that a label be located in a specific space
because that instruction can only operate on data located in that space. A label is assigned
to a space by one of the following methods:
Table 22. Anonymous Labels
Symbol Description
$$ Anonymous label. This symbol can be used as a label an arbitrary number of times.
$B Anonymous label backward reference. This symbol references the most recent anonymous
label defined before the reference.
$F Anonymous label forward reference. This symbol references the most recent anonymous
label defined after the reference.