Datasheet

78K0/Ix2 CHAPTER 10 WATCHDOG TIMER
R01UH0010EJ0500 Rev.5.00 357
Feb 28, 2012
CHAPTER 10 WATCHDOG TIMER
10.1 Functions of Watchdog Timer
The watchdog timer is mounted onto all 78K0/Ix2 microcontroller products.
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 register (detection of an invalid check while the CPU
hangs up)
If the CPU accesses an area that is not set by the IMS register (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, refer to CHAPTER 20 RESET FUNCTION.