PIC16F610 Datasheet, PDF (121/180 Pages) Microchip Technology – 14-Pin, Flash-Based 8-Bit CMOS Microcontrollers

PIC16F610/616/16HV610/616
12.6 Watchdog Timer (WDT)
The Watchdog Timer is a free running, on-chip RC
oscillator, which requires no external components. This
RC oscillator is separate from the external RC oscillator
of the CLKIN pin and INTOSC. That means that the
WDT will run, even if the clock on the OSC1 and OSC2
pins of the device has been stopped (for example, by
execution of a SLEEP instruction). During normal oper-
ation, a WDT time out generates a device Reset. If the
device is in Sleep mode, a WDT time out causes the
device to wake-up and continue with normal operation.
The WDT can be permanently disabled by program-
ming the Configuration bit, WDTE, as clear
(Section 12.1 “Configuration Bits”).
12.6.1 WDT PERIOD
The WDT has a nominal time-out period of 18 ms (with
no prescaler). The time-out periods vary with
temperature, VDD and process variations from part to
part (see Table 15-4, Parameter 31). If longer time-out
periods are desired, a prescaler with a division ratio of
up to 1:128 can be assigned to the WDT under
software control by writing to the OPTION register.
Thus, time-out periods up to 2.3 seconds can be
realized.
The CLRWDT and SLEEP instructions clear the WDT
and the prescaler, if assigned to the WDT, and prevent
it from timing out and generating a device Reset.
The TO bit in the STATUS register will be cleared upon
a Watchdog Timer time out.
12.6.2 WDT PROGRAMMING
CONSIDERATIONS
It should also be taken in account that under worst-
case conditions (i.e., VDD = Min., Temperature = Max.,
Max. WDT prescaler) it may take several seconds
before a WDT time out occurs.
FIGURE 12-2:
CLKOUT
(= FOSC/4)
T0CKI
pin
T0SE
WATCHDOG TIMER BLOCK DIAGRAM
0
1
0
T0CS
1
8-bit
Prescaler
1
SYNC 2
Cycles
0
PSA
Data Bus
8
TMR0
Set Flag bit T0IF
on Overflow
PSA
Watchdog
Timer
8
3
PS<2:0>
1
WDT
Time-Out
0
WDTE
Note 1: T0SE, T0CS, PSA, PS<2:0> are bits in the OPTION register.
PSA
TABLE 12-7: WDT STATUS
Conditions
WDTE = 0
CLRWDT Command
Exit Sleep + System Clock = EXTRC, INTRC, EC
Exit Sleep + System Clock = XT, HS, LP
WDT
Cleared
Cleared until the end of OST
© 2007 Microchip Technology Inc.
Preliminary
DS41288C-page 119