H8SLASH3021 datasheet(102/712 Pages) RENESAS

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4. Exception Handling

Rev.2.00 Mar. 22, 2007 Page 78 of 684

REJ09B0352-0200

4.6

Notes on Stack Usage

When accessing word data or longword data, the H8/3022 Group regards the lowest address bit as

0. The stack should always be accessed by word access or longword access, and the value of the

stack pointer (SP, ER7) should always be kept even. Use the following instructions to save

registers:

PUSH.W Rn

(or MOV.W Rn, @–SP)

PUSH.L ERn

(or MOV.L ERn, @–SP)

Use the following instructions to restore registers:

POP.W Rn

(or MOV.W @SP+, Rn)

POP.L ERn

(or MOV.L @SP+, ERn)

Setting SP to an odd value may lead to a malfunction. Figure 4.5 shows an example of what

happens when the SP value is odd.

TRAPA instruction executed

CCR

Legend

CCR:

PC:

R1L:

SP:

R1L

MOV. B R1L, @-ER7

SP set to H'FFEFF

Data saved above SP

CCR contents lost

Condition code register

Program counter

General register R1L

Stack pointer

Note: The diagram illustrates modes 1, 3, 5, 6, and 7.

H'FFEFA

H'FFEFB

H'FFEFC

H'FFEFD

H'FFEFF

Figure 4.5 Operation when SP Value is Odd

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