41594B datasheet(70/372 Pages) MICROCHIP

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PIC12LF1840T48A

DS41594B-page 70

Preliminary

 2011-2012 Microchip Technology Inc.

7.1

Power-on Reset (POR)

The POR circuit holds the device in Reset until VDD has

reached an acceptable level for minimum operation.

Slow rising VDD, fast operating speeds or analog

performance may require greater than minimum VDD.

The PWRT, BOR or MCLR features can be used to

extend the start-up period until all device operation

conditions have been met.

7.1.1

POWER-UP TIMER (PWRT)

The Power-up Timer provides a nominal 64 ms time-

out on POR or Brown-out Reset.

The device is held in Reset as long as PWRT is active.

The PWRT delay allows additional time for the VDD to

rise to an acceptable level. The Power-up Timer is

enabled by clearing the PWRTE bit in Configuration

Word 1.

The Power-up Timer starts after the release of the POR

and BOR.

For additional information, refer to Application Note

AN607, “Power-up Trouble Shooting” (DS00607).

7.2

Brown-Out Reset (BOR)

The BOR circuit holds the device in Reset when VDD

reaches a selectable minimum level. Between the

POR and BOR, complete voltage range coverage for

execution protection can be implemented.

The Brown-out Reset module has four operating

modes controlled by the BOREN<1:0> bits in Configu-

ration Word 1. The four operating modes are:

• BOR is always on

• BOR is off when in Sleep

• BOR is controlled by software

• BOR is always off

Refer to Table 7-1 for more information.

The Brown-out Reset voltage level is selectable by

configuring the BORV bit in Configuration Word 2.

A VDD noise rejection filter prevents the BOR from trig-

gering on small events. If VDD falls below VBOR for a

duration greater than parameter TBORDC, the device

will reset. See Figure 7-3 for more information.

TABLE 7-1:

BOR OPERATING MODES

7.2.1

BOR IS ALWAYS ON

When the BOREN bits of Configuration Word 1 are set

to ‘11’, the BOR is always on. The device start-up will

be delayed until the BOR is ready and VDD is higher

than the BOR threshold.

BOR protection is active during Sleep. The BOR does

not delay wake-up from Sleep.

7.2.2

BOR IS OFF IN SLEEP

When the BOREN bits of Configuration Word 1 are set

to ‘10’, the BOR is on, except in Sleep. The device

start-up will be delayed until the BOR is ready and VDD

is higher than the BOR threshold.

BOR protection is not active during Sleep. The device

wake-up will be delayed until the BOR is ready.

7.2.3

BOR CONTROLLED BY SOFTWARE

When the BOREN bits of Configuration Word 1 are set

to ‘01’, the BOR is controlled by the SBOREN bit of the

BORCON register. The device start-up is not delayed

by the BOR ready condition or the VDD level.

BOR protection begins as soon as the BOR circuit is

ready. The status of the BOR circuit is reflected in the

BORRDY bit of the BORCON register.

BOR protection is unchanged by Sleep.

BOREN

Config bits

SBOREN

Device Mode

BOR Mode

Device

Operation upon

release of POR

Device

Operation upon

wake- up from

Sleep

BOR_ON (11)

Active

Waits for BOR ready(1)

BOR_NSLEEP (10)

Awake

Active

Waits for BOR ready

BOR_NSLEEP (10)

Sleep

Disabled

BOR_SBOREN (01)

Active

Begins immediately

BOR_SBOREN (01)

Disabled

Begins immediately

BOR_OFF (00)

Disabled

Begins immediately

Note 1: Even though this case specifically waits for the BOR, the BOR is already operating, so there is no delay in

start-up.

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