29.4.7.1 Testing each byte of the counter
The test procedure follows these steps:
1. Program the preferred watchdog timeout value in the TOVAL register during the
watchdog configuration time period.
2. Select a byte of the counter to test using the CS[TST] = 10b for the low byte;
CS[TST] = 11b for the high byte.
3. Wait for the watchdog to timeout. Optionally, in the idle loop, increment RAM
locations as a parallel software counter for later comparison. Because the RAM is not
affected by a watchdog reset, the timeout period of the watchdog counter can be
compared with the software counter to verify the timeout period has occurred as
expected.
4. The watchdog counter times out and forces a reset.
5. Confirm the WDOG flag in the system reset register is set, indicating that the
watchdog caused the reset. (The POR flag remains clear.)
6. Confirm that CS[TST] shows a test (10b or 11b) was performed.
If confirmed, the count and compare functions work for the selected byte. Repeat the
procedure, selecting the other byte in step 2.
NOTE
CS[TST] is cleared by a POR only and not affected by other
resets.
29.4.7.2 Entering user mode
After successfully testing the low and high bytes of the watchdog counter, the user can
configure CS[TST] to 01b to indicate the watchdog is ready for use in application user
mode. Thus if a reset occurs again, software can recognize the reset trigger as a real
watchdog reset caused by runaway or faulty application code.
As an ongoing test when using the default LPO clock source, software can periodically
read the CNT register to ensure the counter is being incremented.
29.5 Application Information
The watchdog is enabled by default after reset. To disable or reconfigure the watchdog, it
is better to be done before the first watchdog timeout. It is suggested to disable or
reconfigure the watchdog at the very beginning of the software code, e.g. beginning of
the startup or main function.
Chapter 29 Watchdog timer (WDOG)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors
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