Watchdog Prescale and Counter
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SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
Timer Module Overview
11.15 Watchdog Prescale and Counter
The watchdog "prescale" is the WD_PERIOD bit field. It sets the counter period for the watchdog to a time
between approximately 17ms typical (14.5ms Min to 20.1ms max) and approximately 2.2 sec typical (1.85
sec Min to 2.6 sec Max). Note that these numbers are for a specific device and a specific version of that
device. Consult the current data sheet for the specific device you are using.
The counter can be reset by writing a 1 to the CNT_RESET bit. When using the watchdog, normally a
write to CNT_RESET is put into the background loop of the program. That way if the program gets lost,
the counter will not get reset, and the watchdog will trigger, resetting the UCD.
The counter output is used by two compare blocks with fixed values.
11.16 Watchdog Compare Blocks
The two compare blocks are one for the counter half full, and one for the counter overflow.
The half full counter interrupt is intended to give advance warning that something is wrong with program
execution. If the interrupt function is still working, it can be used to start a recovery operation.
The counter overflow can also be used just as an interrupt, or it can be configured to reset the CPU.
The configuration is relatively simple, and can be understood from
Note that the Watchdog Wake Event is another name for the Half Compare Event.
The only special bit is the Protect bit.
11.17 Watchdog Protect Bit
The Watchdog Protect but is a special bit. Once it is cleared, it cannot be set again. It also causes other
bits to be set so that they cannot be cleared. The effect is that once the protect bit is cleared, the
watchdog timer cannot be turned off. It will always need to be cleared by writing a 1 to CNT_RESET.
Other bits in the Watchdog Control register are not protected, however. For example, the WD_PERIOD
bits can still be changed, as can the interrupt enable bits. Refer to
for details.