WDOG counter
WDOG_WINH and
WDOG_WINL
Refresh opportunity
in window mode
WDOG_TOVALH and
WDOG_TOVALL
0
Time
Refresh opportunity (not in window mode)
Figure 17-2. Refresh opportunity for the Watchdog counter
17.3.1.1 Window mode
Software finishing its main control loop faster than expected could be an indication of a
problem. Depending on the requirements of the application, the WDOG can be
programmed to force a reset when refresh attempts are early.
When Window mode is enabled, the watchdog must be refreshed after the counter has
reached a minimum expected time value; otherwise, the watchdog resets the MCU. The
minimum expected time value is specified in the WDOG_WINH:L registers. Setting
CS1[WIN] enables Window mode.
17.3.1.2 Refreshing the Watchdog
The refresh write sequence is a write of 0xA602 followed by a write of 0xB480 to the
WDOG_CNTH and WDOG_CNTL registers. The write of the 0xB480 must occur within
16 bus clocks after the write of 0xA602; otherwise, the watchdog resets the MCU.
Functional description
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
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NXP Semiconductors
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