Union directive – Zilog ZUSBOPTS User Manual
Page 270
Directives
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242
Zilog Developer Studio II – ZNEO™
User Manual
Once applied to label tname, the individual structure elements are applied to tname to pro-
duce the desired offsets using tname as the structure base. For example, the label
tname.name_2
is created and assigned the value
tname + stag.name_2
. If there are
any alignment requirements with the structure, the
.TAG
directive attaches the required
alignment to the label. The optional count on the
.TAG
directive is meaningful only inside
a structure definition and implies an array of the
.TAG
structure.
Keeping the space allocation separate allows you to place the
.TAG
declarations that assign
structure to a label in the header file in a similar fashion to the
.STRUCT
and
XREF
direc-
tives. You can then include the header file in multiple source files wherever the label is
used. Make sure to perform the space allocation for the label in only one source file.
Examples of the
.TAG
directive are as follows:
DATE .STRUCT
MONTH DS 1
DAY DS 1
YEAR DS 2
DSIZE .ENDSTRUCT DATE
NAMELEN EQU 30
EMPLOYEE .STRUCT
NAME DS NAMELEN
SOCIAL DS 10
START .TAG DATE
SALARY DS 1
ESIZE .ENDSTRUCT EMPLOYEE
NEWYEARS .TAG DATE
NEWYEARS DS DSIZE
The
.TAG
directive in the last example above creates the symbols
NEWYEARS.MONTH
,
NEWYEARS.DAY
, and
NEWYEARS.YEAR
. The space for
NEWYEARS
is allocated by the
DS
directive.
.UNION Directive
The
.UNION
directive is similar to the
.STRUCT
directive, except that the offset is reset to
zero on each label. A
.UNION
directive cannot have an offset or parent union. The key-
word to terminate a
.UNION
definition is
.ENDSTRUCT
.
Note: