Datasheet

 1999-2012 Microchip Technology Inc. DS40192D-page 35
PIC16C505
7.6.1 WDT PERIOD
The WDT has a nominal time-out period of 18 ms,
(with no prescaler). If a longer time-out period is
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, a time-out
period of a nominal 2.3 seconds can be realized.
These periods vary with temperature, V
DD and part-to-
part process variations (see DC specs).
Under worst case conditions (V
DD = Min., Temperature
= Max., max. WDT prescaler), it may take several
seconds before a WDT time-out occurs.
7.6.2 WDT PROGRAMMING CONSIDERATIONS
The CLRWDT instruction clears the WDT and the
postscaler, if assigned to the WDT, and prevents it
from timing out and generating a device RESET.
The SLEEP instruction resets the WDT and the
postscaler, if assigned to the WDT. This gives the
maximum SLEEP time before a WDT wake-up reset.
FIGURE 7-11: WATCHDOG TIMER BLOCK DIAGRAM
TABLE 7-6: SUMMARY OF REGISTERS ASSOCIATED WITH THE WATCHDOG TIMER
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Value on
Power-On
Reset
Value on
All Other
Resets
N/A OPTION
RBWU RBPU T0CS T0SE PSA PS2 PS1 PS0 1111 1111 1111 1111
Legend: Shaded boxes = Not used by Watchdog Timer, — = unimplemented, read as '0', u = unchanged.
1
0
1
0
From Timer0 Clock Source
(Figure 6-5)
To Timer0 (Figure 6-4)
Postscaler
WDT Enable
Configuration Bit
PSA
WDT
Time-out
PS<2:0>
PSA
MUX
8 - to - 1 MUX
Postscaler
M
U
X
Watchdog
Timer
Note: T0CS, T0SE, PSA, PS<2:0>
are bits in the OPTION register.