PIC16LC712 datasheet(57/106 Pages) MICROCHIP

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 1999-2013 Microchip Technology Inc.

DS41106C-page 57

PIC16C712/716

FIGURE 9-8:

EXTERNAL BROWN-OUT

PROTECTION CIRCUIT 1

FIGURE 9-9:

EXTERNAL BROWN-OUT

PROTECTION CIRCUIT 2

FIGURE 9-10:

EXTERNAL BROWN-OUT

PROTECTION CIRCUIT 3

9.8

Time-out Sequence

On power-up the time-out sequence is as follows: First

PWRT time-out is invoked after the POR time delay has

expired. Then OST is activated. The total time-out will

vary based on oscillator configuration and the status of

the PWRT. For example, in RC mode with the PWRT

disabled, there will be no time-out at all. Figure 9-11,

Figure 9-12,

and

Figure 9-13

depict

time-out

sequences on power-up.

Since the time-outs occur from the POR pulse, if MCLR

is kept low long enough, the time-outs will expire. Then

bringing MCLR high will begin execution immediately

(Figure 9-13). This is useful for testing purposes or to

synchronize more than one PIC16CXXX device

operating in parallel.

Table 9-5 shows the Reset conditions for some Special

Function Registers, while Table 9-6 shows the Reset

conditions for all the registers.

Note 1: This circuit will activate Reset when

VDD goes below (Vz + 0.7V) where

Vz = Zener voltage.

2: Internal Brown-out Reset circuitry

should be disabled when using this

circuit.

VDD

33k

10k

40k

VDD

MCLR

PIC16C7XX

Note 1: This brown-out circuit is less expensive,

albeit less accurate. Transistor Q1 turns

off when VDD is below a certain level

such that:

2: Internal Brown-out Reset should be

disabled when using this circuit.

3: Resistors should be adjusted for the

characteristics of the transistor.

VDD x

R1 + R2

= 0.7V

VDD

40k

VDD

MCLR

PIC16C7XX

This

brown-out

protection

circuit

employs

Microchip Technology’s MCP809 microcontroller

supervisor. The MCP8XX and MCP1XX families

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 accommodate 5V and 3V systems

MCLR

PIC16C7XX

VDD

Vss

RST

MCP809

VDD

bypass

capacitor

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