Tiene un oscilador RC independiente del principal, cuyo periodo es de 18ms.
Esto está extraído de la página 121 de
este datasheet.
12.6 Watchdog Timer (WDT)The Watchdog Timer is a free running, on-chip RC
oscillator, which requires no external components. This
RC oscillator is separate from the external RC oscillator
of the CLKIN pin and INTOSC. That means that the
WDT will run, even if the clock on the OSC1 and OSC2
pins of the device has been stopped (for example, by
execution of a SLEEP instruction). During normal operation, a WDT time out generates a device Reset. If the
device is in Sleep mode, a WDT time out causes the
device to wake-up and continue with normal operation.
The WDT can be permanently disabled by programming the Configuration bit, WDTE, as clear
(Section 12.1 “Configuration Bits”).
12.6.1 WDT PERIODThe WDT has a nominal time-out period of 18 ms (with
no prescaler). The time-out periods vary with
temperature, VDD and process variations from part to
part (see DC specs). If longer time-out periods are
desired, a prescaler with a division ratio of up to 1:128
can be assigned to the WDT under software control by
writing to the OPTION register. Thus, time-out periods
up to 2.3 seconds can be realized.
The CLRWDT and SLEEP instructions clear the WDT
and the prescaler, if assigned to the WDT, and prevent
it from timing out and generating a device Reset.
The TO bit in the STATUS register will be cleared upon
a Watchdog Timer time out.