ST9291 datasheet(17/20 Pages) STMICROELECTRONICS

17 / 20 page

Stack location

Care is necessary when managing stacks as there

is no limit to stack sizes apart from the bottom of

any address space in which the stack is placed.

Consequently programmers are advised to use a

stack pointer value as high as possible, particularly

when using the Register File as a stacking area.

This will also benefit programmers who may locate

the stacks in group D using, for example the in-

struction ld R237, #223 which loads the value

SYSTEM REGISTERS (Continued)

STACK POINTER L

STACK

VA00434

R255

STACK POINTER H

Figure 1-11. System and/or User Stack in

STACK POINTER L

SYSTEM REGISTERS

STACK

DATA MEMORY

VA00435

STACK POINTER H

Figure 1-12. System and/or User Stack in

Memory Stack Mode

223 into the User Stack Pointer Low Register. The

Programmer will not need to remember to set the

in the D-group, a problem outlined in Register

Pointing Techniques paragraph.

Stacks may be located anywhere in the first 14

groups of the Register File (internal stacks) or the

data memory (external stacks). It is not necessary

to set the data memory using the instruction sdm

as external stack instructions automatically use the

data memory.

USP R236 (ECh) System Read/Write

User Stack Pointer High Byte

Reset value: undefined

USP15USP14 USP13USP12USP11 USP10 USP9 USP8

USP R237 (EDh) System Read/Write

User Stack Pointer Low Byte

Reset value: undefined

USP7 USP6 USP5 USP4 USP3 USP2 USP1 USP0

SSP R238 (EEh) System Read/Write

System Stack Pointer High Byte

Reset value: undefined

SSP15 SSP14 SSP13SSP12 SSP11SSP10 SSP9 SSP8

SSP R239 (EFh) System Read/Write

System Stack Pointer Low Byte

Reset value: undefined

SSP7 SSP6 SSP5 SSP4 SSP3 SSP2 SSP1 SSP0

1.2 MEMORY

ST9291

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