AN1218 datasheet(10/56 Pages) FREESCALE

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Application Note

AN1218 Rev. 2

Index Registers

CPU08 has the additional H index register which is the high byte

extension to the X index register. Together, the two index registers

formulate the concatenated 16-bit H:X index register. Five new

instructions are introduced on the CPU08 to allow manipulation of the

H:X index register. Source code written for the HC05 will not effect the

H register and it will remain in its reset state of $00.

The TSX and the TXS instructions also utilize the H:X index register.

These instructions are covered in more detail in the stack pointer

section.

Five New Indexing

Instructions, Detail

The new CPU08 instructions that affect the index registers are listed

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

CPU08 Indexing Instruction Examples

AIX

Add Immediate to Index Register

Operation:

X ← (H:X) + (M)

Description: AIX adds an immediate value to the 16-bit

index register formed by the concatenation

of the H and X registers. The immediate

operand is an 8-bit two's complement

signed offset. Prior to addition to H:X, the

offset is sign extended to 16 bits.

CLRH

Clear Index High

Operation:

H ← $00

Description: The contents of H are replaced with zeros.

CPHX

Compare 16-bit Index Register

Operation:

(H:X) – (M:M+1)

Description: CPHX compares the 16-bit index register

H:X with the 16-bit value in memory and

sets the condition code register accordingly.

Freescale Semiconductor, Inc.

For More Information On This Product,

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