Notes On Use Of The Stack - Hitachi H8S/2646 Hardware Manual

4.7

Notes on Use of the Stack

When accessing word data or longword data, the H8S/2646 Series assumes that the lowest address
bit is 0. The stack should always be accessed by word transfer instruction or longword transfer
instruction, and the value of the stack pointer (SP, ER7) should always be kept even. Use the
following instructions to save registers:
PUSH.W Rn
PUSH.L ERn
Use the following instructions to restore registers:
POP.W Rn
POP.L ERn
Setting SP to an odd value may lead to a malfunction. Figure 4-6 shows an example of what
happens when the SP value is odd.
SP
TRAPA instruction executed
SP set to H'FFFEFF
Legend
Note: This diagram illustrates an example in which the interrupt control mode
is 0, in advanced mode.
(or MOV.W Rn, @-SP)
(or MOV.L ERn, @-SP)
(or MOV.W @SP+, Rn)
(or MOV.L @SP+, ERn)
SP
Data saved above SP
CCR: Condition code register
PC: Program counter
R1L: General register R1L
SP: Stack pointer
Figure 4-6 Operation when SP Value is Odd
SP
CCR
PC
MOV.B R1L, @–ER7
Contents of CCR lost
R1L H'FFFEFA
H'FFFEFB
PC
H'FFFEFC
H'FFFEFD
H'FFFEFF
99