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CHAPTER 12 INTERRUPT FUNCTIONS
User’s Manual U15104EJ2V0UD
12.4.2 Maskable interrupt request acknowledgement operation
A maskable interrupt request becomes acknowledgeable when the interrupt request flag is set to 1 and the mask
(MK) flag of the interrupt request is cleared to 0. A vectored interrupt request is acknowledged in an interrupt enable
state (with IE flag set to 1). However, a low-priority interrupt request is not acknowledged during high-priority interrupt
servicing (with ISP flag reset to 0).
Wait times from maskable interrupt request generation to interrupt request servicing are as follows.
For the interrupt acknowledge timing, refer to Figures 12-11 and 12-12.
Table 12-3. Times from Maskable Interrupt Request Generation to Interrupt Servicing
Minimum Time
Maximum Time
Note
When
××
PR
= 0
7 clocks
32 clocks
When
××
PR
= 1
8 clocks
33 clocks
Note
If an interrupt request is generated just before a divide instruction, the wait
time is maximized.
Remark 1 clock:
(f
CPU
: CPU clock)
If two or more maskable interrupt requests are generated simultaneously, the request specified for higher priority
with the priority specification flag is acknowledged first. If two or more requests are specified as the same priority
by the priority specification flag, the default priorities apply.
Any pending interrupt requests are acknowledged when they become acknowledgeable.
Figure 12-10 shows interrupt request acknowledgement algorithms.
If a maskable interrupt request is acknowledged, the acknowledged interrupt request is saved to the stack, the
program status word (PSW) and the program counter (PC), in that order, the IE flag is reset to 0, and the acknowledged
interrupt priority specification flag contents are transferred to the ISP flag. Further, the vector table data determined
for each interrupt request is loaded into the PC and branched.
Return from the interrupt is possible with the RETI instruction.
f
CPU
1