Chapter 3 Interrupts

3-1-3 Operation

Interrupt Processing Sequence

For interrupts other than reset, the interrupt processing sequence consists of interrupt request, interrupt acceptance, and hardware processing. The program counter (PC) and processor status word (PSW) and handy addressing data (HA) are saved onto the stack, and execution branches to the address specified by the corresponding interrupt vector.

An interrupt handler ends by restoring the contents of any registers used during processing and then executing the return from interrupt (RTI) instruction to return to the point at which execution was inter- rupted.

 

 

Interrupt service routine

Main program

 

 

 

Interrupt

 

 

 

 

Hardware processing

 

 

request (xxxIR)

 

 

 

flag cleared

 

Save up PC, PSW, etc.

 

 

 

 

 

at head

 

 

 

 

Interrupt

Max. 12 machine cycles

11 machine cycles

Restart

Restore PSW, PC up, etc.

 

 

RTI

Figure 3-1-2 Interrupt Processing Sequence (maskable interrupts)

Overview III - 5

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Panasonic F77G, MN101C77C user manual Operation, Rti