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CHAPTER 18
INTERRUPT FUNCTIONS
User’s Manual U12790EJ2V0UD
18.4.2 Maskable interrupt request acknowledgment operation
A maskable interrupt request becomes acknowledgeable when an 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 enabled
state (with the IE flag set to 1). However, a low-priority interrupt request is not acknowledged during high-priority
interrupt servicing (with the ISP flag reset to 0).
The wait times from maskable interrupt request generation to interrupt request servicing are as follows.
For the interrupt acknowledgment timing, refer to Figures 18-11 and 18-12.
Table 18-3. 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 :
(fCPU: CPU clock)
If two or more maskable interrupt requests are generated simultaneously, the request specified as having a priority
by the priority specification flag is acknowledged first. If two or more requests are specified as having the same priority
by the priority specification flag, the default priorities apply.
Any pending interrupt requests are acknowledged when they become acknowledgeable.
Figure 18-10 shows the interrupt request acknowledgment algorithms.
If a maskable interrupt request is acknowledged, the acknowledged interrupt request is saved in 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 using the RETI instruction.
fCPU
1