PIC12F508_09 datasheet(54/110 Pages) MICROCHIP

54 / 110 page

PIC12F508/509/16F505

DS41236E-page 54

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 7-12 and

Figure 7-13.

FIGURE 7-12:

BROWN-OUT

PROTECTION CIRCUIT 1

FIGURE 7-13:

BROWN-OUT

PROTECTION CIRCUIT 2

FIGURE 7-14:

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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