PIC12C5XX
8.7
Time-Out Sequence, Power Down,
and Wake-up from SLEEP Status Bits
(TO/PD/GPWUF)
FIGURE 8-14: BROWN-OUT PROTECTION
CIRCUIT 2
VDD
The TO, PD, and GPWUF bits in the STATUS register
can be tested to determine if a RESET condition has
been caused by a power-up condition, a MCLR or
Watchdog Timer (WDT) reset.
VDD
VDD
R1
Q1
MCLR
TABLE 8-7:
TO/PD/GPWUF STATUS
AFTER RESET
R2
40k*
PIC12C5XX
GPWUF TO PD
RESET caused by
WDT wake-up from
0
0
0
0
0
1
0
u
0
SLEEP
WDT time-out (not from
SLEEP)
This brown-out circuit is less expensive, although
less accurate. Transistor Q1 turns off when VDD
is below a certain level such that:
MCLR wake-up from
SLEEP
R1
= 0.7V
0
0
1
1
u
1
1
u
0
Power-up
VDD •
R1 + R2
MCLR not during SLEEP
*Refer to Figure 8-7 and Table 11-1 for internal
weak pull-up on MCLR.
Wake-up from SLEEP on
pin change
Legend: u = unchanged
Note 1: The TO, PD, and GPWUF bits maintain
their status (u) until a reset occurs. A low-
pulse on the MCLR input does not change
the TO, PD, and GPWUF status bits.
FIGURE 8-15: BROWN-OUT PROTECTION
CIRCUIT 3
VDD
8.8
Reset on Brown-Out
MCP809
VDD
bypass
capacitor
Vss
A brown-out is a condition where device power (VDD)
dips below its minimum value, but not to zero, and then
recovers. The device should be reset in the event of a
brown-out.
VDD
RST
MCLR
PIC12C5XX
To reset PIC12C5XX devices when
a brown-out
occurs, external brown-out protection circuits may be
This brown-out protection circuit employs
Microchip Technology’s MCP809 microcontroller
supervisor. The MCP8XX and MCP1XX family of
supervisors provide push-pull and open collector
outputs with both high and low active reset pins.
There are 7 different trip point selections to
accomodate 5V and 3V systems.
built, as shown in Figure 8-13
Figure 8-15
, Figure 8-14 and
FIGURE 8-13: BROWN-OUT PROTECTION
CIRCUIT 1
VDD
VDD
VDD
33k
Q1
10k
MCLR
40k*
PIC12C5XX
This circuit will activate reset when VDD goes below
Vz + 0.7V (where Vz = Zener voltage).
*Refer to Figure 8-7 and Table 11-1 for internal
weak pull-up on MCLR.
DS40139E-page 44
1999 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
