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Chapter 2 Basic CPU Functions
32
Interrupts
■ Operation when Returning from Interrupt
After the program POPs the register and other values saved by the interrupt service
routine, an RTI instruction is implemented to return to the program that was being
executed when the interrupt was received.
The processing sequence for the return from interrupt instruction, RTI, is listed
below.
1. The processor status word (PSW) is pulled from the stack. (SP)
2. The program counter(PC = return address) is pulled from the stack. (SP+1
to
3)
3. The handy address register (HA) is pulled from the stack. (SP+4, 5)
4. The SP is pulled. (SP+6 → SP)
5. Execution branches to the address indicated by the PC.