PIC18CXX2
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.
18.2
Watchdog Timer (WDT)
The Watchdog Timer is a free running on-chip RC oscil-
lator, which does not require any external components.
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 SLEEPinstruction.
Note: The CLRWDTand SLEEPinstructions clear
the WDT and the postscaler if assigned to
the WDT, and prevent it from timing out and
generating a device RESET condition.
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.
Note: When a CLRWDT instruction is executed
and the prescaler is assigned to the WDT,
the prescaler count will be cleared, but the
prescaler assignment is not changed.
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.
18.2.1 CONTROL REGISTER
Register 18-7 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 18-7 WDTCON Register
U-0
U-0
U-0
U-0
U-0
U-0
U-0
R/W-0
SWDTEN
bit 0
—
—
—
—
—
—
—
bit 7
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
7/99 Microchip Technology Inc.
Preliminary
DS39026B-page 185
MICROCHIP [ MICROCHIP ]
