This situation differs depending on whether the watchdog timer interrupts are being used as NMI or as ordinary (maskable) interrupts.
The corresponding bit in ISPR is set to 0 when the watchdog timer interrupts are used as ordinary interrupts. Perform the following processing in this event:
(2) Check ISPR. When the corresponding bit is set to "1", execute a RETI instruction.
(3) When the corresponding bit in ISPR becomes "0", branch to the reset processing block.
When the watchdog timer interrupts are used as NMI, the PSW.NP bit is set to "0" where no more interrupts can be acknowledged.
If a maskable interrupt is being serviced when an NMI occurs, the bit in ISPR register corresponding to that interrupt is set to "1."
Clear the NP bit first, and then perform the processing steps (1) to (3) shown above.
The following is a specific program sample.