PIC12CE519-04SLASHESM datasheet(44/113 Pages) MICROCHIP

44 / 113 page

PIC12C5XX

DS40139E-page 44

8.7

Time-Out Sequence, Power Down,

and Wake-up from SLEEP Status Bits

(TO/PD/GPWUF)

The TO, PD, and GPWUF 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.

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 PIC12C5XX devices when a brown-out

occurs, external brown-out protection circuits may be

built, as shown in Figure 8-13 , Figure 8-14 and

Figure 8-15

FIGURE 8-13: BROWN-OUT PROTECTION

CIRCUIT 1

TABLE 8-7:

TO/PD/GPWUF STATUS

AFTER RESET

GPWUF

RESET caused by

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

Legend: u = unchanged

Note 1: The TO, PD, and GPWUF bits maintain

their status (u) until a reset occurs. A low-

pulse on the MCLR input does not change

the TO, PD, and GPWUF status bits.

This circuit will activate reset when VDD goes below

Vz + 0.7V (where Vz = Zener voltage).

*Refer to Figure 8-7 and Table 11-1 for internal

weak pull-up on MCLR.

33k

10k

40k*

MCLR

PIC12C5XX

VDD

FIGURE 8-14: BROWN-OUT PROTECTION

CIRCUIT 2

FIGURE 8-15: BROWN-OUT PROTECTION

CIRCUIT 3

This brown-out circuit is less expensive, although

less accurate. Transistor Q1 turns off when VDD

is below a certain level such that:

*Refer to Figure 8-7 and Table 11-1 for internal

weak pull-up on MCLR.

VDD •

R1 + R2

= 0.7V

40k*

MCLR

PIC12C5XX

VDD

This

brown-out

protection

circuit

employs

Microchip Technology’s MCP809 microcontroller

supervisor. The MCP8XX and MCP1XX family of

supervisors provide push-pull and open collector

outputs with both high and low active reset pins.

There are 7 different trip point selections to

accomodate 5V and 3V systems.

MCLR

PIC12C5XX

VDD

Vss

RST

MCP809

VDD

bypass

capacitor

PIC12CE519-04/ESM Datasheet(PDF) 44 Page - Microchip Technology

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