PIC12CE519-04I Datasheet, PDF (44/113 Pages) Microchip Technology – 8-Pin, 8-Bit CMOS Microcontrollers

PIC12C5XX
8.7 Time-Out Sequence, Power Down,
and Wake-up from SLEEP Status Bits
(TO/PD/GPWUF)
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.
TABLE 8-7: TO/PD/GPWUF STATUS
AFTER RESET
GPWUF TO PD
RESET caused by
0
0 0 WDT wake-up from
SLEEP
0
0 u WDT time-out (not from
SLEEP)
0
1 0 MCLR wake-up from
SLEEP
0
1 1 Power-up
0
u u MCLR not during SLEEP
1
1 0 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.
8.8 Reset on Brown-Out
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.
To reset PIC12C5XX devices when a brown-out
occurs, external brown-out protection circuits may be
built, as shown in Figure 8-13 , Figure 8-14 and
Figure 8-15
FIGURE 8-13: BROWN-OUT PROTECTION
CIRCUIT 1
VDD
33k
10k
VDD
VDD
Q1
MCLR
40k* _PIC12C5XX
FIGURE 8-14: BROWN-OUT PROTECTION
CIRCUIT 2
VDD
VDD
VDD
R1
Q1
MCLR
R2
40k* _PIC12C5XX
This brown-out circuit is less expensive, although
less accurate. Transistor Q1 turns off when VDD
is below a certain level such that:
VDD •
R1
= 0.7V
R1 + R2
*Refer to Figure 8-7 and Table 11-1 for internal
weak pull-up on MCLR.
FIGURE 8-15: BROWN-OUT PROTECTION
CIRCUIT 3
VDD
MCP809 _bypass
Vss
capacitor
VDD
RST
VDD
MCLR
PIC12C5XX
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.
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.