PIC16F526 Datasheet, PDF (55/122 Pages) Microchip Technology – 14-Pin, 8-Bit Flash Microcontroller

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
CWUF RBWUF TO PD Reset Caused By
0
0
0 0 WDT wake-up from
Sleep
0
0
0 u WDT time-out (not from
Sleep)
0
0
1 0 MCLR wake-up from
Sleep
0
0
1 1 Power-up
0
0
u u MCLR not during Sleep
0
1
1 0 Wake-up from Sleep on
pin change
1
0
1 0 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.
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.
PIC16F526
FIGURE 8-12:
VDD
33k
10k
BROWN-OUT
PROTECTION CIRCUIT 1
VDD
PIC12F510
PIC16F506
Q1 _MCLR(2)
40k⁽¹⁾
Note 1:
2:
This circuit will activate Reset when VDD goes
below Vz + 0.7V (where Vz = Zener voltage).
Pin must be configured as MCLR.
FIGURE 8-13:
VDD
R1
R2
BROWN-OUT
PROTECTION CIRCUIT 2
VDD
PIC12F510
PIC16F506
Q1 _MCLR(2)
40k⁽¹⁾
Note 1:
2:
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
Pin must be configured as MCLR.
FIGURE 8-14:
BROWN-OUT
PROTECTION CIRCUIT 3
VDD
MCP809 _Bypass
VSS
Capacitor
VDD
RST
VDD
MCLR
PIC12F510
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.
 2010 Microchip Technology Inc.
DS41326D-page 55