M054LAN Datasheet, PDF (40/64 Pages) Nuvotem Talema – ARM Cortex™-M0 32-BIT MICROCONTROLLER

M052/M054 Data Sheet
6.9 Watchdog Timer (WDT)
6.9.1 Overview
The purpose of Watchdog Timer is to perform a system reset when system runs into an unknown
state. This prevents system from hanging for an infinite period of time. Besides, this Watchdog
Timer supports another function to wakeup CPU from power-down mode. The watchdog timer
includes a 18-bit free running counter with programmable time-out intervals. Table 6–4 shows the
watchdog timeout interval selection and Figure 6–14 shows the timing of watchdog interrupt
signal and reset signal.
Setting WTE (WDTCR [7]) enables the watchdog timer and the WDT counter starts counting up.
When the counter reaches the selected time-out interval, Watchdog timer interrupt flag WTIF will
be set immediately to request a WDT interrupt if the watchdog timer interrupt enable bit WTIE is
set, in the meanwhile, a specified delay time (1024 * T_WDT) follows the time-out event. User must
set WTR (WDTCR [0]) (Watchdog timer reset) high to reset the 18-bit WDT counter to avoid CPU
from Watchdog timer reset before the delay time expires. WTR bit is cleared automatically by
hardware after WDT counter is reset. There are eight time-out intervals with specific delay time
which are selected by Watchdog timer interval select bits WTIS (WDTCR [10:8]). If the WDT
counter has not been cleared after the specific delay time expires, the watchdog timer will set
Watchdog Timer Reset Flag (WTRF) high and reset CPU. This reset will last 63 WDT clocks
(T_RST) then CPU restarts executing program from reset vector (0x0000 0000). WTRF will not be
cleared by Watchdog reset. User may poll WTFR by software to recognize the reset source. WDT
also provides wakeup function. When chip is powered down and the Watchdog Timer Wakeup
Function Enable bit (WDTR[4]) is set, if the WDT counter has not been cleared after the specific
delay time expires, the chip will be waken up from power down state.
WTIS
000
001
010
011
100
101
110
111
Timeout Interval
Selection
T_TIS
2⁴ * T_WDT
2⁶ * T_WDT
2⁸ * T_WDT
2¹⁰ * T_WDT
2¹² * T_WDT
2¹⁴ * T_WDT
2¹⁶ * T_WDT
2¹⁸ * T_WDT
Interrupt Period
T_INT
1024 * T_WDT
1024 * T_WDT
1024 * T_WDT
1024 * T_WDT
1024 * T_WDT
1024 * T_WDT
1024 * T_WDT
1024 * T_WDT
WTR Timeout Interval
(WDT_CLK=10 kHz)
Min. T_WTR ~ Max. T_WTR
1.6 ms ~ 104 ms
6.4 ms ~ 108.8 ms
25.6 ms ~ 128 ms
102.4 ms ~ 204.8 ms
409.6 ms ~ 512 ms
1.6384 s ~ 1.7408 s
6.5536 s ~ 6.656 s
26.2144 s ~ 26.3168 s
Table 6–4 Watchdog Timeout Interval Selection
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Publication Release Date: Mar 15, 2011
Revision V1.0