
2002 Microchip Technology Inc.
Preliminary
DS40044A-page 107
PIC16F627A/628A/648A
FIGURE 14-16:
WATCHDOG TIMER BLOCK DIAGRAM
TABLE 14-9:
SUMMARY OF WATCHDOG TIMER REGISTERS
14.8
Power-Down Mode (SLEEP)
The Power-down mode is entered by executing a
SLEEP
instruction.
If enabled, the Watchdog Timer will be cleared but
keeps running, the PD bit in the STATUS register is
cleared, the TO bit is set, and the oscillator driver is
turned off. The I/O ports maintain the status they had,
before
SLEEP
was executed (driving high, low, or hi-
impedance).
For lowest current consumption in this mode, all I/O
pins should be either at V
DD
, or V
SS
, with no external
circuitry drawing current from the I/O pin and the com-
parators, and V
REF
should be disabled. I/O pins that
are hi-impedance inputs should be pulled high or low
externally to avoid switching currents caused by float-
ing inputs. The T0CKI input should also be at V
DD
or
V
SS
for lowest current consumption. The contribution
from on chip pull-ups on PORTB should be considered.
The MCLR pin must be at a logic high level (V
IHMC
).
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
POR Reset
Value on all
other
RESETS
2007h
Config.
bits
LVP
BOREN
MCLRE
FOSC2
PWRTE
WDTE
FOSC1
FOSC0
uuuu uuuu
uuuu uuuu
81h, 181h
OPTION
RBPU
INTEDG
T0CS
T0SE
PSA
PS2
PS1
PS0
1111 1111
1111 1111
Legend:
x = unknown, u = unchanged, - = unimplemented read as '0', q = value depends upon condition.
Note:
Shaded cells are not used by the Watchdog Timer.
(Figure 6-1)
Note:
T0SE, T0CS, PSA, PS0-PS2 are bits in the OPTION register.
From TMR0 Clock Source
Watchdog
Timer
WDT
Enable Bit
0
1
8
8 to 1 MUX
PS<2:0>
To TMR0
(Figure 6-1)
0
1
PSA
WDT
Time out
PSA
M
U
X
MUX
3
WDT POSTSCALER/
TMR0 PRESCALER
Note:
It should be noted that a RESET generated
by a WDT time out does not drive MCLR
pin low.