PIC16F688-ISLASHML datasheet(117/204 Pages) MICROCHIP

117 / 204 page

DS41203E-page 115

PIC16F688

11.2.5

TIME-OUT SEQUENCE

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

PWRT time-out is invoked after POR has expired, then

OST is activated after the PWRT time-out has expired.

The total time-out will vary based on oscillator configu-

ration and PWRTE bit status. For example, in EC mode

with PWRTE bit erased (PWRT disabled), there will be

no time-out at all. Figure 11.2.1, Figure 11-5 and

Figure 11-6 depict time-out sequences. The device can

execute code from the INTOSC while OST is active by

enabling Two-Speed Start-up or Fail-Safe Monitor (see

Section 3.7.2 “Two-Speed Start-up Sequence” and

Section 3.8 “Fail-Safe Clock Monitor”).

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

(see Figure 11-5). This is useful for testing purposes or

to synchronize more than one PIC16F688 device

operating in parallel.

Table 11-5 shows the Reset conditions for some

special registers, while Table 11-4 shows the Reset

conditions for all the registers.

11.2.6

POWER CONTROL (PCON)

The Power Control (PCON) register (address 8Eh) has

two Status bits to indicate what type of Reset that last

occurred.

Bit 0 is BOR (Brown-out). BOR is unknown on

Power-on Reset. It must then be set by the user and

checked on subsequent Resets to see if BOR = 0,

indicating that a Brown-out has occurred. The BOR

Status bit is a “don’t care” and is not necessarily

predictable

the

brown-out

circuit

disabled

(BOREN<1:0>

= 00 in the Configuration Word

Bit 1 is POR (Power-on Reset). It is a ‘0’ on Power-on

Reset and unaffected otherwise. The user must write a

‘1’ to this bit following a Power-on Reset. On a

subsequent Reset, if POR is ‘0’, it will indicate that a

Power-on Reset has occurred (i.e., VDD may have

gone too low).

For more information, see Section 4.2.4 “Ultra

Low-Power

Wake-up”

and

Section 11.2.4

“Brown-Out Reset (BOR)”.

TABLE 11-1:

TIME-OUT IN VARIOUS SITUATIONS

TABLE 11-2:

PCON BITS AND THEIR SIGNIFICANCE

TABLE 11-3:

SUMMARY OF REGISTERS ASSOCIATED WITH BROWN-OUT RESET

Oscillator Configuration

Power-up

Brown-out Reset

Wake-up

from Sleep

PWRTE = 0

PWRTE = 1

PWRTE = 0

PWRTE = 1

XT, HS, LP

TPWRT + 1024

• TOSC

1024 • TOSC

TPWRT + 1024

• TOSC

1024 • TOSC

RC, EC, INTOSC

TPWRT

—TPWRT

——

POR

BOR

Condition

0u11

Power-on Reset

1011

Brown-out Reset

uu0u

WDT Reset

uu00

WDT Wake-up

uuuu

MCLR Reset during normal operation

uu10

MCLR Reset during Sleep

Legend: u = unchanged, x = unknown

Name

Bit 9

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on

POR, BOR

Value on

all other

Resets(1)

CONFIG(2)

BOREN1

BOREN0

CPD

MCLRE

PWRTE

WDTE

FOSC2

FOSC1

FOSC0

—

PCON

—

ULPWUE SBOREN

—

—POR

BOR

--01 --qq

--0u --uu

STATUS

IRP

RP1

RP0

0001 1xxx

000q quuu

Legend:

= unchanged, x = unknown, – = unimplemented bit, reads as ‘0’, q = value depends on condition. Shaded cells are not used by BOR.

Note

Other (non Power-up) Resets include MCLR Reset and Watchdog Timer Reset during normal operation.

See Configuration Word register (Register 11-1) for operation of all register bits.

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