HD6433644R datasheet(98/549 Pages) RENESAS

98 / 549 page

Section 3 Exception Handling

Rev. 6.00 Sep 12, 2006 page 78 of 526

REJ09B0326-0600

3.4

Application Notes

3.4.1

Notes on Stack Area Use

When word data is accessed in the H8/3644 Group, the least significant bit of the address is

regarded as 0. Access to the stack always takes place in word size, so the stack pointer (SP: R7)

should never indicate an odd address. Use PUSH Rn (MOV.W Rn, @–SP) or POP Rn (MOV.W

@SP+, Rn) to save or restore register values.

Setting an odd address in SP may cause a program to crash. An example is shown in figure 3.6.

R1L

H'FEFC

H'FEFD

H'FEFF

→

MOV. B R1L, @–R7

SP set to H'FEFF

Stack accessed beyond SP

BSR instruction

Contents of PC are lost

Legend:

PCH:

PCL:

R1L:

SP:

Upper byte of program counter

Lower byte of program counter

General register R1L

Stack pointer

Figure 3.6 Operation when Odd Address Is Set in SP

When CCR contents are saved to the stack during interrupt exception handling or restored when

RTE is executed, this also takes place in word size. Both the upper and lower bytes of word data

are saved to the stack; on return, the even address contents are restored to CCR while the odd

address contents are ignored.

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