Notes On Stack Usage - Hitachi H8/3048 Hardware Manual

4.6 Notes on Stack Usage

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When accessing word data or longword data, the H8/3048 Series 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 4-7 shows an example of what
happens when the SP value is odd.
SP
TRAPA instruction executed
SP set to H'FFFEFF
Legend
CCR: Condition code register
PC: Program counter
R1L: General register R1L
SP: Stack pointer
Note: The diagram illustrates modes 3 and 4.
CCR
SP
PC
Data saved above SP
Figure 4-7 Operation when SP Value is Odd
80
SP R1L
PC
MOV. B R1L, @-ER7
CCR contents lost
H'FFFEFA
H'FFFEFB
H'FFFEFC
H'FFFEFD
H'FFFEFF