Datasheet

 2010 Microchip Technology Inc. DS41326E-page 55
PIC16F526
8.7 Time-out Sequence, Power-down
and Wake-up from Sleep Status
Bits (TO
, PD, RBWUF, CWUF)
The TO, PD and RBWUF 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/RBWUF/CWUF
STATUS AFTER RESET
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 PIC16F526 devices when a brown-out occurs,
external brown-out protection circuits may be built, as
shown in Figure 8-12 and Figure 8-13.
FIGURE 8-12: BROWN-OUT
PROTECTION CIRCUIT 1
FIGURE 8-13: BROWN-OUT
PROTECTION CIRCUIT 2
FIGURE 8-14: BROWN-OUT
PROTECTION CIRCUIT 3
CWUF RBWUF TO PD Reset Caused By
0000WDT wake-up from
Sleep
000uWDT time-out (not from
Sleep)
0010MCLR
wake-up from
Sleep
0011Power-up
00uuMCLR not during Sleep
0110Wake-up from Sleep on
pin change
1010
Wake up from Sleep on
comparator change
Legend: u = unchanged
Note 1: The TO, PD and RBWUF bits maintain
their status (u) until a Reset occurs. A
low-pulse on the MCLR input does not
change the TO
, PD and RBWUF Status
bits.
Note 1: This circuit will activate Reset when VDD goes
below Vz + 0.7V (where Vz = Zener voltage).
2: Pin must be configured as MCLR
.
33k
10k
40k
(1)
VDD
MCLR
(2)
PIC12F510
VDD
Q1
PIC16F506
Note 1: This brown-out circuit is less expensive,
although less accurate. Transistor Q1 turns
off when V
DD is below a certain level such
that:
2: Pin must be configured as MCLR
.
V
DD •
R1
R1 + R2
= 0.7V
R2
40k
(1)
VDD
MCLR
(2)
PIC12F510
R1
Q1
VDD
PIC16F506
Note: This brown-out protection circuit employs
Microchip Technology’s MCP809 microcon-
troller supervisor. There are 7 different trip
point selections to accommodate 5V to 3V
systems.
MCLR
PIC12F510
VDD
VDD
VSS
RST
MCP809
VDD
Bypass
Capacitor
PIC16F506