PM0223 datasheet(52/110 Pages) STMICROELECTRONICS

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The STM32L0 Cortex-M0+ Instruction Set

PM0223

52/110

DocID025763 Rev 1

3.4.6

PUSH and POP

Push registers onto, and pop registers off a full-descending stack.

Syntax

PUSH reglist

POP reglist

where:

Operation

PUSH

stores registers on the stack, with the lowest numbered register using the lowest

memory address and the highest numbered register using the highest memory address.

POP

loads registers from the stack, with the lowest numbered register using the lowest

memory address and the highest numbered register using the highest memory address.

PUSH

uses the value in the SP register minus four as the highest memory address, POP

uses the value in the SP register as the lowest memory address, implementing a full-

descending stack. On completion, PUSH updates the SP register to point to the location of

the lowest store value, POP updates the SP register to point to the location above the

highest location loaded.

If a POP instruction includes PC in its reglist, a branch to this location is performed when

the POP instruction has completed. Bit[0] of the value read for the PC is used to update the

APSR T-bit. This bit must be 1 to ensure correct operation.

Restrictions

In these instructions:

•

reglist

must use only R0-R7.

•

The exception is LR for a PUSH and PC for a POP.

Condition flags

These instructions do not change the flags.

Examples

PUSH

{R0,R4-R7}

; Push R0,R4,R5,R6,R7 onto the stack

PUSH

{R2,LR}

; Push R2 and the link-register onto the stack

POP

{R0,R6,PC}

; Pop r0,r6 and PC from the stack, then branch to

; the new PC.

reglist

Is a non-empty list of registers, enclosed in braces. It can contain register

ranges. It must be comma separated if it contains more than one register or

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