NXP Semiconductors K22F series, Reference Manual, Page: 526 / 1407

1. Select either quick test or byte test..
2. Set a certain test mode bit to put the watchdog in the functional test mode. Setting
this bit automatically switches the watchdog timer to a fast clock source. The
switching of the clock source is done to achieve a faster time-out and hence a faster
test.
In a successful test, the timer times out after reaching the programmed time-out value and
generates a system reset.
Note
After emerging from a reset due to a watchdog test, unlock and
configure the watchdog. The refresh and unlock operations and
interrupt are not automatically disabled in the test mode.
24.4.1 Quick test
In this test, the time-out value of watchdog timer is programmed to a very low value to
achieve quick time-out. The only difference between the quick test and the normal mode
of the watchdog is that TESTWDOG is set for the quick test. This allows for a faster test
of the watchdog reset mechanism.
24.4.2 Byte test
The byte test is a more thorough a test of the watchdog timer. In this test, the timer is split
up into its constituent byte-wide stages that are run independently and tested for time-out
against the corresponding byte of the time-out value register. The following figure
explains the splitting concept:
Testing the watchdog
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
526 NXP Semiconductors