12F508 Microchip Technology, 12F508 Datasheet - Page 53

• Manufacturer Part Number: 12F508
• Description: Search -----> PIC12F508
• Manufacturer: Microchip Technology

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7.7
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:
7.8
A brown-out is a condition where device power (V
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:
© 2005 Microchip Technology Inc.
Legend: u = unchanged
Note 1:
Note 1:
GPWUF/
RBWUF
0
0
0
0
0
1
33k
2:
V
Time-out Sequence, Power-down
and Wake-up from Sleep Status
Bits (TO, PD, GPWUF/RBWUF)
Reset on Brown-out
DD
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.
This circuit will activate Reset when V
below Vz + 0.7V (where Vz = Zener voltage).
Pin must be confirmed as MCLR.
TO
0
0
1
1
u
1
10k
TO/PD/(GPWUF/RBWUF)
STATUS AFTER RESET
PD
0
u
0
1
u
0
BROWN-OUT
PROTECTION CIRCUIT 1
Q1
40k
WDT wake-up from Sleep
WDT time-out (not from
Sleep)
MCLR wake-up from Sleep
Power-up
MCLR not during Sleep
Wake-up from Sleep on pin
change
MCLR
(1)
V
DD
Reset Caused By
(2)
PIC16F505
PIC12F508
PIC12F509
DD
goes
Preliminary
DD
)
PIC12F508/509/16F505
FIGURE 7-14:
FIGURE 7-15:
Note 1:
Note:
V
2:
SS
MCP809
RST
R1
R2
This brown-out circuit is less expensive,
although less accurate. Transistor Q1 turns
off when V
that:
Pin must be confirmed as MCLR.
V
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.
DD
V
V
V
DD
DD
DD
Capacitor
•
Bypass
DD
BROWN-OUT
PROTECTION CIRCUIT 2
BROWN-OUT
PROTECTION CIRCUIT 3
R1 + R2
is below a certain level such
R1
Q1
40k
V
DD
MCLR
(1)
= 0.7V
V
PIC16F505
PIC12F508
PIC12F509
DD
DS41236B-page 51
(2)
PIC16F505
PIC12F508
PIC12F509
MCLR