PIC18F258-ESLASHLSQTP datasheet(274/402 Pages) MICROCHIP

274 / 402 page

PIC18FXX8

DS41159E-page 272

24.2

Watchdog Timer (WDT)

The Watchdog Timer is a free running, on-chip RC

oscillator which does not require any external com-

ponents. This RC oscillator is separate from the RC

oscillator of the OSC1/CLKI pin. That means that the

WDT will run, even if the clock on the OSC1/CLKI and

OSC2/CLKO/RA6 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 (Watchdog Timer Reset). If the device is

in Sleep mode, a WDT time-out causes the device to

wake-up

and

continue

with

normal

operation

(Watchdog Timer wake-up). The TO bit in the RCON

The Watchdog Timer is enabled/disabled by a device

configuration bit. If the WDT is enabled, software

execution may not disable this function. When the

WDTEN configuration bit is cleared, the SWDTEN bit

enables/disables the operation of the WDT.

The WDT time-out period values may be found in

Section 27.0

“Electrical

Characteristics”

under

parameter #31. Values for the WDT postscaler may be

assigned using the configuration bits.

24.2.1

CONTROL REGISTER

readable and writable register which contains a control

bit that allows software to override the WDT enable

configuration bit only when the configuration bit has

disabled the WDT.

Note:

The CLRWDT and SLEEP instructions clear

the WDT and the postscaler if assigned to

the WDT and prevent it from timing out

and generating a device Reset condition.

Note:

When a CLRWDT instruction is executed

and the postscaler is assigned to the WDT,

the postscaler count will be cleared but the

postscaler assignment is not changed.

U-0

R/W-0

—

—SWDTEN

bit 7

bit 0

bit 7-1

Unimplemented: Read as ‘0’

bit 0

SWDTEN: Software Controlled Watchdog Timer Enable bit

= Watchdog Timer is on

= Watchdog Timer is turned off if the WDTEN configuration bit in the Configuration register = 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

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