
2002 Microchip Technology Inc.
DS41120B-page 129
PIC16C717/770/771
12.12 Watchdog Timer (WDT)
The Watchdog Timer is a free running on-chip RC oscil-
lator, which does not require any external components.
This oscillator is independent from the processor clock.
If enabled, the WDT will run even if the main clock of
the device has been stopped, for example, by execu-
tion 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 STATUS regis-
ter will be cleared upon a Watchdog Timer time-out.
The WDT can be permanently disabled by program-
WDT time-out period values may be found in
Table 15-4. Values for the WDT prescaler may be assigned using
the OPTION_REG register.
FIGURE 12-11:
WATCHDOG TIMER BLOCK DIAGRAM
TABLE 12-7:
SUMMARY OF WATCHDOG TIMER REGISTERS
Note:
The SLEEP instruction clears the WDT and
the postscaler, if assigned to the WDT,
restarting the WDT period.
From TMR0 Clock Source
Postscaler
WDT Timer
WDT
Enable Bit(2)
0
1
M
U
X
PSA
8 - to - 1 MUX
PS<2:0>(1)
0
1
MUX
PSA(1)
WDT
Time-out
Note 1: PSA and PS<2:0> are bits in the OPTION_REG register.
8
2: WDTE bit in the configuration word.
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
2007h
Config. bits(1)
—
BODEN
MCLRE
PWRTE
WDTE
FOSC2
FOSC1
FOSC0
81h,181h
OPTION_REG
RBPU
INTEDG
T0CS
T0SE
PSA
PS2
PS1
PS0
Legend: Shaded cells are not used by the Watchdog Timer.
Note 1: See
Register 12-1 for the full description of the configuration word bits.