Datasheet

© 2005 Microchip Technology Inc. Preliminary DS41236B-page 51
PIC12F508/509/16F505
7.7 Time-out Sequence, Power-down
and Wake-up from Sleep Status
Bits (TO
, PD, GPWUF/RBWUF)
The TO, PD and (GPWUF/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 7-8: TO/PD/(GPWUF/RBWUF)
STATUS AFTER RESET
7.8 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 PIC12F508/509/16F505 devices when a
brown-out occurs, external brown-out protection
circuits may be built, as shown in Figure 7-13 and
Figure 7-14.
FIGURE 7-13: BROWN-OUT
PROTECTION CIRCUIT 1
FIGURE 7-14: BROWN-OUT
PROTECTION CIRCUIT 2
FIGURE 7-15: BROWN-OUT
PROTECTION CIRCUIT 3
GPWUF/
RBWUF
TO
PD Reset Caused By
000WDT wake-up from Sleep
00uWDT time-out (not from
Sleep)
010MCLR
wake-up from Sleep
011Power-up
0uuMCLR
not during Sleep
110Wake-up from Sleep on pin
change
Legend: u = unchanged
Note 1: The TO
, PD and GPWUF/RBWUF bits
maintain their status (u) until a Reset
occurs. A low-pulse on the MCLR input
does not change the TO
, PD and
GPWUF/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 confirmed as MCLR
.
33k
10k
40k
(1)
VDD
MCLR
(2)
PIC16F505
VDD
Q1
PIC12F508
PIC12F509
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 confirmed as MCLR
.
V
DD •
R1
R1 + R2
= 0.7V
R2
40k
(1)
VDD
MCLR
(2)
PIC16F505
R1
Q1
VDD
PIC12F508
PIC12F509
Note: This brown-out protection circuit employs
Microchip Technology’s MCP809 micro-
controller supervisor. There are 7 different
trip point selections to accommodate 5V to
3V systems.
MCLR
PIC16F505
VDD
VDD
VSS
RST
MCP809
VDD
Bypass
Capacitor
PIC12F508
PIC12F509