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4.8 Usage
Note
When accessing word data or longword data, this LSI 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 (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 4.4 shows an example of what
happens when the SP value is odd.
SP
CCR :
PC :
R1L :
SP :
Condition code register
Program counter
General register R1L
Stack pointer
CCR
SP
SP
R1L
H'FFFEFA
H'FFFEFB
H'FFFEFC
H'FFFEFD
H'FFFEFE
H'FFFEFF
PC
PC
TRAP instruction executed
SP set to H'FFFEFF
Data saved above SP
MOV.B R1L, @-ER7 instruction executed
Contents of CCR lost
Address
Legend
Note: This diagram illustrates an example in which the interrupt control mode is 0, in advanced mode.
Figure 4.4 Operation when SP Value Is Odd
Summary of Contents for H8S/2627
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