81
PC and CCR
saved to stack
SP (R7)
SP – 1
SP – 2
SP – 3
SP – 4
Stack area
SP + 4
SP + 3
SP + 2
SP + 1
SP (R7)
Even address
Prior to start of interrupt
exception handling
After completion of interrupt
exception handling
Notation:
PC
H
:
PC
L
:
CCR:
SP:
Upper 8 bits of program counter (PC)
Lower 8 bits of program counter (PC)
Condition code register
Stack pointer
Notes:
CCR
CCR
PC
H
PC
L
1.
2.
*
PC shows the address of the first instruction to be executed upon
return from the interrupt handling routine.
Register contents must always be saved and restored by word access,
starting from an even-numbered address.
Ignored on return.
*
Figure 3.4 Stack State after Completion of Interrupt Exception Handling
Figure 3.5 shows a typical interrupt sequence.