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ManualsBrandsRENESAS ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller SSOP 30 8-Bit 10 MHz I/O number 21
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78K0/Kx2-L CHAPTER 17 INTERRUPT FUNCTIONS
R01UH0028EJ0400 Rev.4.00 629
Sep 27, 2010
17.4 Interrupt Servicing Operations
17.4.1 Maskable interrupt acknowledgment
A maskable interrupt becomes acknowledgeable when the interrupt request flag is set to 1 and the mask (MK) flag
corresponding to that interrupt request is cleared to 0. A vectored interrupt request is acknowledged if interrupts are in the
interrupt enabled state (when the IE flag is set to 1). However, a low-priority interrupt request is not acknowledged during
servicing of a higher priority interrupt request (when the ISP flag is reset to 0).
The times from generation of a maskable interrupt request until vectored interrupt servicing is performed are listed in
Table 17-4 below.
For the interrupt request acknowledgment timing, refer to Figures 17-26 and 17-27.
Table 17-4. Time from Generation of Maskable Interrupt Until 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 becomes longer.
Remark 1 clock: 1/f
CPU (fCPU: CPU clock)
If two or more maskable interrupt requests are generated simultaneously, the request with a higher priority level
specified in the priority specification flag is acknowledged first. If two or more interrupts requests have the same priority
level, the request with the highest default priority is acknowledged first.
An interrupt request that is held pending is acknowledged when it becomes acknowledgeable.
Figure 17-25 shows the interrupt request acknowledgment algorithm.
If a maskable interrupt request is acknowledged, the contents are saved into the stacks in the order of PSW, then PC,
the IE flag is reset (0), and the contents of the priority specification flag corresponding to the acknowledged interrupt are
transferred to the ISP flag. The vector table data determined for each interrupt request is the loaded into the PC and
branched.
Restoring from an interrupt is possible by using the RETI instruction.