CHAPTER 14 INTERRUPT FUNCTIONS
Figure 14-13. Interrupt Request Acknowledgment Timing (Example: MOV A, r)
8 clocks
Clock
Saving PSW and PC, and
jump to interrupt servicing
MOV A, r
Interrupt servicing program
CPU
Interrupt
If the interrupt request has generated an interrupt request flag (XXIF) by the time the instruction clocks under
execution, n clocks (n = 4 to 10), are n − 1, interrupt request acknowledgment processing will start following the
completion of the instruction under execution. Figure 14-13 shows an example using the 8-bit data transfer
instruction MOV A, r. Because this instruction is executed in 4 clocks, if an interrupt request is generated between
the start of execution and the 3rd clock, interrupt request acknowledgment processing will take place following the
completion of MOV A, r.
Figure 14-14. Interrupt Request Acknowledgment Timing
(When Interrupt Request Flag Is Generated in Final Clock Under Execution)
8 clocks
Clock
Interrupt servicing
program
Saving PSW and PC, and
jump to interrupt servicing
NOP
MOV A, r
CPU
Interrupt
If the interrupt request flag (XXIF) is generated in the final clock of the instruction, interrupt request
acknowledgment processing will begin after execution of the next instruction is complete.
Figure 14-14 shows an example whereby an interrupt request was generated in the 2nd clock of NOP (a 2-clock
instruction). In this case, the interrupt request will be processed after execution of MOV A, r, which follows NOP, is
complete.
Caution When interrupt request flag registers 0 and 1 (IF0 and IF1), or interrupt mask flag registers 0 and
1 (MK0 and MK1) are being accessed, interrupt requests will be held pending.
14.4.3 Multiple interrupt servicing
Multiple interrupts, in which another interrupt request is acknowledged while an interrupt request being serviced,
can be serviced using the priority order. If multiple interrupts are generated at the same time, they are serviced in
the order according to the priority assigned to each interrupt request in advance (refer to Table 14-1).
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