Texas Instruments TMS320C54x, User Manual

Page: 173 / 469

.union/.endunion/.tag
Declare Union Type
4-90
Syntax
[ utag ] .union [ expr ]
[ mem
0
] element [ expr
0
]
[ mem
1
] element [ expr
1
]
. . .
. . .
. . .
[ mem
n
] .tag utag
n
[, expr
n
]
. . .
. . .
. . .
[ mem
N
] element [ expr
N
]
[ size ] .endunion
label
.tag
utag
Description The .union directive assigns symbolic offsets to the elements of alternate data
structure definitions to be allocated in the same memory space. This enables
you to define several alternate structures and then let the assembler calculate
the element offset. This is similar to a C union. The .union directive does not
allocate any memory; it merely creates a symbolic template that can be used
repeatedly.
A .struct definition may contain a .union definition, and .structs and .unions
may be nested.
The .endunion directive terminates the union definition.
The .tag directive gives structure or union characteristics to a label, simplifying
the symbolic representation and providing the ability to define structures or
unions that contain other structures or unions. The .tag directive does not allo-
cate memory. The structure or union tag of a .tag directive must have been pre-
viously defined.