Datasheet

PIC18FXX8
DS41159E-page 272 © 2006 Microchip Technology Inc.
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
register will be cleared upon a WDT time-out.
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
Register 24-13 shows the WDTCON register. This is a
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.
REGISTER 24-13: WDTCON: WATCHDOG TIMER CONTROL REGISTER
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 U-0 U-0 U-0 U-0 U-0 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
1 = Watchdog Timer is on
0 = 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