AT32UC3L064_2 Datasheet, PDF (285/830 Pages) ATMEL Corporation – 32-bit AVR® Microcontroller

AT32UC3L016/32/64
16.5.2
Window Mode
The window mode can protect against tight loops of runaway code. This is obtained by adding a
ban period to timeout period. During the ban period clearing the WDT counter is not allowed.
If the WDT Mode (MODE) bit in the CTRL Register is one, the WDT is in window mode. Note
that the CTRL.MODE bit can only be changed when the WDT is disabled (CTRL.EN=0).
The PSEL and Time Ban Prescale Select (TBAN) fields in the CTRL Register selects the WDT
timeout period
T_timeout = T_tban + T_psel = (2^(TBAN+1) + 2^(PSEL+1)) / f_{clk_cnt}
where T_tban sets the time period when clearing the WDT counter by writing to the CLR.WDTCLR
bit is not allowed. Doing so will result in a watchdog reset, the device will receive a reset and the
code will start executing form the boot vector, see Figure 16-5 on page 286. The WDT counter
will be cleared.
Writing a one to the CLR.WDTCLR bit within the T_psel period will clear the WDT counter and the
counter starts counting from zero (t=t₀), entering T_tban, see Figure 16-4 on page 285.
If the value in the CTRL Register is changed, the WDT counter will be cleared without a watch-
dog reset, regardless of if the value in the WDT counter and the TBAN value.
If the WDT counter reaches T_timeout, the counter will be cleared, the device will receive a reset
and the code will start executing form the boot vector.
Figure 16-4. Window Mode WDT Timing Diagram
t=t₀
T_tban
T_psel
Timeout
Write one to
CLR.WDTCLR
Watchdog reset
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