Zilog ZUSBOPTS Manuel d'utilisateur télécharger pdf (Page 268)

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101

Directives UM017105-0511

240

Zilog Developer Studio II – ZNEO™

User Manual

.STRUCT and .ENDSTRUCT Directives

A structure is a collection of various elements grouped together under a single name for

convenient handling. The

.STRUCT and .ENDSTRUCT directives can be used to define the

layout for a structure in assembly by identifying the various elements and their sizes. The

.STRUCT directive assigns symbolic offsets to the elements of a structure. It does not allo-

cate memory. It merely creates a symbolic template that can be used repeatedly.

The

.STRUCT and .ENDSTRUCT directives have the following form:

[stag]

.STRUCT [offset | : parent]

[name_1]

DS count1

[name_2]

DS count2

[tname]

.TAG stagx [count]

...

[name_n]

DS count3

[ssize]

.ENDSTRUCT [stag]

The label stag defines a symbol to use to reference the structure; the expression offset, if

used, indicates a starting offset value to use for the first element encountered; otherwise,

the starting offset defaults to zero.

If parent is specified rather than offset, the parent must be the name of a previously

defined structure, and the offset is the size of the parent structure. In addition, each name

in the parent structure is inserted in the new structure.

Each element can have an optional label, such as name_1, which is assigned the value of

the element’s offset into the structure and which can be used as the symbolic offset. If stag

is missing, these element names become global symbols; otherwise, they are referenced

using the syntax

stag.name. The directives following the optional label can be any space

reserving directive such as

DS, or the .TAG directive (defined below), and the structure

offset is adjusted accordingly.

The label ssize, if provided, is a label in the global name space and is assigned the size of

the structure.

If a label stag is specified with the

.ENDSTRUCT directive, it must match the label that is

used for the

.STRUCT directive. The intent is to allow for code readability with some

checking by the assembler.

An example structure definition is:

DATE

.STRUCT

MONTH DS 1

DAY

DS 1

1 2 ... 263 264 265 266 267 268 269 270 271 272 273 ... 519 520

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Zilog ZUSBOPTS Manuel d'utilisateur Page 268

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