AN1218 datasheet(13/56 Pages) FREESCALE

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Application Note

Stack Pointer

AN1218 Rev. 2

requirements are also reduced. Significant C code efficiency can be

gained when utilizing these new stack pointer addressing modes.

If interrupts are disabled, the stack pointer can be used as a second

16-bit index register with 8- or 16-bit offsets.

Nine New Stack

Manipulation

Instructions, Detail

All the new CPU08 instructions that affect the stack pointer are listed

below. Examples for these instructions are given in AppendixC—New

CPU08 Stack Pointer Instructions

AIS

Add Immediate to Stack Pointer

Operation:

SP ← (SP) + (M)

Description: Adds the immediate operand to the stack

pointer SP. The immediate value is an 8-bit

two's complement signed operand. Prior to

addition to the SP, the operand is sign

extended to 16 bits. This instruction can be

used to create and remove a stack frame

buffer which is used to store temporary

variables.

PSHA

Push Accumulator onto Stack

Operation:

⇓ (A); SP ← (SP-$01)

Description: The contents of the accumulator are pushed

onto the stack at the address contained in

the stack pointer. The stack pointer is then

decremented to point at the next available

location in the stack. The contents of the

accumulator remain unchanged.

PSHH

Push Index Register H onto Stack

Operation:

⇓ (H); SP ← (SP-$01)

Description: The contents of the 8-bit high order index

address contained in the stack pointer. The

stack pointer is then decremented to point at

the next available location in the stack. The

contents of the H register remain

unchanged.

Freescale Semiconductor, Inc.

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