Interrupt Request Acknowledgment Processing Algorithm - NEC PD789860 User Manual

Figure 14-8. Interrupt Request Acknowledgment Processing Algorithm
××IF:
Interrupt request flag
××MK:
Interrupt mask flag
IE: Flag to control maskable interrupt request acknowledgment (1 = enable, 0 = disable)
Figure 14-9. Interrupt Request Acknowledgment Timing (Example of MOV A, r)
Clock
CPU
Interrupt
If an interrupt request flag (××IF) is set before an instruction clock n (n = 4 to 10) under execution becomes n − 1,
the interrupt is acknowledged after the instruction under execution is complete. Figure 14-9 shows an example of the
interrupt request acknowledgment timing for an 8-bit data transfer instruction MOV A, r. Since this instruction is
executed for 4 clocks, if an interrupt occurs for 3 clocks after the execution starts, the interrupt acknowledgment
processing is performed after the MOV A, r instruction is executed.
144
CHAPTER 14 INTERRUPT FUNCTIONS
Start
No
××IF = 1?
Yes (Interrupt request generated)
××MK = 0?
Yes
IE = 1?
Yes
Vectored interrupt
servicing
Saving PSW and PC, jump
MOV A, r
User's Manual U14826EJ5V0UD
No
Interrupt request pending
No
Interrupt request pending
8 clocks
Interrupt servicing program
to interrupt servicing