Figure 4-8. Example of Damage Caused by Setting an Odd Address in R7
Although the CCR consists of only one byte, it is treated as word data when pushed on the stack.
In the hardware interrupt exception-handling sequence, two identical CCR bytes are pushed onto
the stack to make a complete word. When popped from the stack by an RTE instruction, the CCR
is loaded from the byte stored at the even address. The byte stored at the odd address is ignored.
PC
H
R1
SP
SP
SP
L
PC
L
PC
H'FECD
H'FECF
H'FECC
BSR instruction
MOV.B R1L, @–R7
PC is improperly stored
beyond top of stack
H'FECF set in SP
PC is lost
H
PC : Upper byte of program counter
Lower byte of program counter
General register
Stack pointer
PC :
R1 :
SP :
H
L
L
L
74
Summary of Contents for H8/326 Series
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