ARM VERSION 1.2 User Manual

Page 63

Writing ARM and Thumb Assembly Language

ARM DUI 0068B

2-51

2.10

Describing data structures with MAP and FIELD directives

You can use the

MAP

and

FIELD

directives to describe data structures. These directives are

always used together.

Data structures defined using

MAP

and

FIELD

•

are easily maintainable

•

can be used to describe multiple instances of the same structure

•

make it easy to access data efficiently.

The

MAP

directive specifies the base address of the data structure. Refer to MAP on

page 7-15 for further information.

The

FIELD

directive specifies the amount of memory required for a data item, and can

give the data item a label. It is repeated for each data item in the structure. Refer to
FIELD on page 7-16 for further information.

Note

No space in memory is allocated when a map is defined. Use define constant directives
(for example,

DCD

) to allocate space in memory.