PIC18F258 Datasheet, PDF (270/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN

PIC18FXX8
24.2 Watchdog Timer (WDT)
The Watchdog Timer is a free running, on-chip RC
oscillator, which does not require any external compo-
nents. This RC oscillator is separate from the RC oscil-
lator 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 (Watch-
dog 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 exe-
cution may not disable this function. When the WDTEN
configuration bit is cleared, the SWDTEN bit enables/
disables the operation of the WDT.
REGISTER 24-13: WDTCON REGISTER
U-0
U-0
U-0
—
—
—
bit 7
The WDT time-out period values may be found in the
Electrical Specifications section under parameter #31.
Values for the WDT postscaler may be assigned using
the configuration bits.
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.
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.
U-0
U-0
U-0
U-0
R/W-0
—
—
—
—
SWDTEN
bit 0
bit 7-1
bit 0
Unimplemented: Read as ’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 reset
DS41159B-page 268
Preliminary
 2002 Microchip Technology Inc.