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CHAPTER 11 WATCHDOG TIMER11.1 Watchdog Timer Functions
The watchdog timer has the following functions.
Watchdog timer
Interval timer
Caution Select the watchdog timer mode or the interval timer mode with the watchdog timer mode register
(WDTM) (The watchdog timer and interval timer cannot be used at the same time).
(1) Watchdog timer mode
An inadvertent program loop (runaway) is detected. Upon detection of the runaway, a non-maskable interrupt
request or RESET can be generated.
Table 11-1. Watchdog Timer Runaway Detection Times
Runaway Detection Time MCS = 1 MCS = 0
211 × 1/fXX 211 × 1/fX (410
µ
s) 212 × 1/fX (819
µ
s)
212 × 1/fXX 212 × 1/fX (819
µ
s) 213 × 1/fX (1.64 ms)
213 × 1/fXX 213 × 1/fX (1.64 ms) 214 × 1/fX (3.28 ms)
214 × 1/fXX 214 × 1/fX (3.28 ms) 215 × 1/fX (6.55 ms)
215 × 1/fXX 215 × 1/fX (6.55 ms) 216 × 1/fX (13.1 ms)
216 × 1/fXX 216 × 1/fX (13.1 ms) 217 × 1/fX (26.2 ms)
217 × 1/fXX 217 × 1/fX (26.2 ms) 218 × 1/fX (52.4 ms)
219 × 1/fXX 219 × 1/fX (104.9 ms) 220 × 1/fX (209.7 ms)
Remarks 1. fXX : Main system clock frequency (fX or fX/2)
2. fX: Main system clock oscillation frequency
3. MCS : Bit 0 of oscillation mode selection register (OSMS)
4. Figures in parentheses apply to operation with fX = 5.0 MHz.