PIC12F508 datasheet(53/98 Pages) MICROCHIP

53 / 98 page

 2004 Microchip Technology Inc.

Preliminary

DS41236A-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

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

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/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

This circuit will activate Reset when VDD goes

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

Pin must be confirmed as MCLR.

33k

10k

40k(1)

VDD

MCLR(2)

PIC16F505

VDD

PIC12F508

PIC12F509

Note

This brown-out circuit is less expensive,

although less accurate. Transistor Q1 turns

off when VDD is below a certain level such

that:

Pin must be confirmed as MCLR.

VDD •

R1 + R2

= 0.7V

40k(1)

VDD

MCLR(2)

PIC16F505

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

VSS

RST

MCP809

VDD

Bypass

Capacitor

PIC12F508

PIC12F509

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