PIC16F84A datasheet(46/124 Pages) MICROCHIP

46 / 124 page

PIC16F8X

DS30430C-page 46

8.7

Time-out Sequence and Power-down

Status Bits (TO/PD)

On power-up (Figure 8-10, Figure 8-11, Figure 8-12

and Figure 8-13) the time-out sequence is as follows:

First PWRT time-out is invoked after a POR has

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

will vary based on oscillator conﬁguration and PWRTE

conﬁguration bit status. For example, in RC mode with

the PWRT disabled, there will be no time-out at all.

TABLE 8-5

TIME-OUT IN VARIOUS

SITUATIONS

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

MCLR is kept low long enough, the time-outs will

expire. Then bringing MCLR high, execution will begin

immediately (Figure 8-10). This is useful for testing

purposes or to synchronize more than one PIC16F8X

device when operating in parallel.

Table 8-6 shows the signiﬁcance of the TO and PD bits.

Table 8-3 lists the reset conditions for some special

registers, while Table 8-4 lists the reset conditions for

all the registers.

TABLE 8-6

STATUS BITS AND THEIR

SIGNIFICANCE

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 a PIC16F8X device when a brown-out occurs,

external brown-out protection circuits may be built, as

shown in Figure 8-14 and Figure 8-15.

FIGURE 8-14: BROWN-OUT PROTECTION

CIRCUIT 1

FIGURE 8-15: BROWN-OUT PROTECTION

CIRCUIT 2

Oscillator

Conﬁguration

Power-up

Wake-up

from

SLEEP

PWRT

Enabled

PWRT

Disabled

XT, HS, LP

72 ms +

1024TOSC

72 ms

—

Condition

Power-on Reset

Illegal, TO is set on POR

Illegal, PD is set on POR

WDT Reset (during normal operation)

WDT Wake-up

MCLR Reset during normal operation

MCLR Reset during SLEEP or interrupt

wake-up from SLEEP

This circuit will activate reset when VDD goes below

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

VDD

33k

10k

40k

VDD

MCLR

PIC16F8X

This brown-out circuit is less expensive, although less

accurate. Transistor Q1 turns off when VDD is below a

certain level such that:

VDD •

R1 + R2

= 0.7V

40k

VDD

MCLR

PIC16F8X

VDD

PIC16F84A Datasheet(PDF) 46 Page - Microchip Technology

PIC16F84A Datasheet(HTML) 46 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL