Chapter 11 Watchdog Timer; Functions Of Watchdog Timer - NEC 78K0 Series User Manual

11.1 Functions of Watchdog Timer

The watchdog timer operates on the internal low-speed oscillation clock.
The watchdog timer is used to detect an inadvertent program loop. If a program loop is detected, an internal reset
signal is generated.
Program loop is detected in the following cases.
• If the watchdog timer counter overflows
• If a 1-bit manipulation instruction is executed on the watchdog timer enable register (WDTE)
• If data other than "ACH" is written to WDTE
• If data is written to WDTE during a window close period
• If the instruction is fetched from an area not set by the IMS and IXS registers (detection of an invalid check while
the CPU hangs up)
• If the CPU accesses an area that is not set by the IMS and IXS registers (excluding FB00H to FFFFH) by
executing a read/write instruction (detection of an abnormal access during a CPU program loop)
When a reset occurs due to the watchdog timer, bit 4 (WDTRF) of the reset control flag register (RESF) is set to 1.
For details of RESF, see CHAPTER 22 RESET FUNCTION.

CHAPTER 11 WATCHDOG TIMER

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