P12C508 datasheet(34/84 Pages) MICROCHIP

34 / 84 page

PIC12C5XX

DS40139A-page 34

Advanced Information

7.7

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, or a MCLR or WDT

reset.

These STATUS bits are only affected by events listed

in Table 7-7.

Table 7-4 lists the reset conditions for the special

function registers, while Table 7-3 lists the reset

conditions for all the registers.

TABLE 7-6:

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:

Legend: u = unchanged

Note 1:

The TO, PD, and GPWUF bits main-

tain their status (u) until a reset

occurs. A low-pulse on the MCLR

input does not change the TO, PD,

and GPWUF status bits.

TABLE 7-7:

EVENTS AFFECTING TO/PD

STATUS BITS

Event

GPWUF

Remarks

Power-up

WDT Time-out

No effect

on PD

SLEEP instruction

CLRWDT

instruction

Wake-up from

SLEEP on pin

change

Legend: u = unchanged

A WDT time-out will occur regardless of the status of the

TO bit. A SLEEP instruction will be executed, regardless of

the status of the PD bit. Table 7-6 reﬂects the status of TO

and PD after the corresponding event.

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 PIC12C5XX 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

This circuit will activate reset when VDD goes below Vz +

0.7V (where Vz = Zener voltage).

*Refer to Figure 7-7 and Table 10-5 for internal weak pull-

up on MCLR.

33k

10k

40k*

VDD

MCLR

PIC12C5XX

VDD

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 7-7 and Table 10-5 for internal weak

pull-up on MCLR.

VDD •

R1 + R2

= 0.7V

40k

VDD

MCLR

PIC12C5XX

VDD

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