PIC12F508/509/16F505
FIGURE 7-14:
BROWN-OUT
PROTECTION CIRCUIT 2
7.7
Time-out Sequence, Power-down
and Wake-up from Sleep Status
Bits (TO, PD, GPWUF/RBWUF)
VDD
VDD
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.
R1
R2
PIC16F505
PIC12F508
PIC12F509
Q1
(2)
MCLR
(1)
40k
TABLE 7-8:
TO/PD/(GPWUF/RBWUF)
STATUS AFTER RESET
GPWUF/
RBWUF
TO PD
Reset Caused By
Note 1: This brown-out circuit is less expensive,
although less accurate. Transistor Q1 turns
off when VDD is below a certain level such
that:
0
0
0
0
0
u
WDT wake-up from Sleep
WDT time-out (not from
Sleep)
R1
= 0.7V
VDD •
0
0
0
1
1
1
u
1
0
1
u
0
MCLR wake-up from Sleep
Power-up
R1 + R2
2: Pin must be confirmed as MCLR.
MCLR not during Sleep
Wake-up from Sleep on pin
change
FIGURE 7-15:
BROWN-OUT
PROTECTION CIRCUIT 3
Legend: u= unchanged
VDD
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
MCP809
VDD
Bypass
Capacitor
VSS
VDD
GPWUF/RBWUF Status bits.
RST
MCLR
PIC16F505
PIC12F508
PIC12F509
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.
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.
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
VDD
VDD
33k
PIC16F505
PIC12F508
PIC12F509
Q1
(2)
MCLR
10k
(1)
40k
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.
© 2007 Microchip Technology Inc.
Preliminary
DS41236C-page 51
MICROCHIP [ MICROCHIP ]
