UPD78F1502AGK-GAK-AX Datasheet, PDF (780/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 19 INTERRUPT FUNCTIONS
19.4 Interrupt Servicing Operations
19.4.1 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.
The times from generation of a maskable interrupt request until vectored interrupt servicing is performed are listed in
Table 19-4 below.
For the interrupt request acknowledgment timing, see Figures 19-15 and 19-16.
Table 19-4. Time from Generation of Maskable Interrupt Until Servicing
Servicing time
Minimum Time
9 clocks
Maximum Time^Note
14 clocks
Note If an interrupt request is generated just before the RET instruction, the wait time becomes longer.
Remark 1 clock: 1/fCLK (fCLK: 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 19-14 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 ISP1 and ISP0 flags. 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.
R01UH0004EJ0501 Rev.5.01
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Jun 20, 2011