DSPIC30F0010AT-20ESLASHS datasheet(157/236 Pages) MICROCHIP

157 / 236 page

DS70150C-page 155

dsPIC30F6010A/6015

FIGURE 21-5:

TIME-OUT SEQUENCE ON POWER-UP (MCLR NOT TIED TO VDD): CASE 2

21.3.1.1

POR with Long Crystal Start-up Time

(with FSCM Enabled)

The oscillator start-up circuitry is not linked to the POR

circuitry. Some crystal circuits (especially low frequency

crystals) will have a relatively long start-up time. There-

fore, one or more of the following conditions is possible

after the POR timer and the PWRT have expired:

• The oscillator circuit has not begun to oscillate.

• The Oscillator Start-up Timer has NOT expired (if

a crystal oscillator is used).

• The PLL has not achieved a LOCK (if PLL is

used).

If the FSCM is enabled and one of the above conditions

is true, then a clock failure trap will occur. The device

will automatically switch to the FRC oscillator and the

user can switch to the desired crystal oscillator in the

trap ISR.

21.3.1.2

Operating without FSCM and PWRT

If the FSCM is disabled and the Power-up Timer

(PWRT) is also disabled, then the device will exit rapidly

from Reset on power-up. If the clock source is FRC,

LPRC, EXTRC or EC, it will be active immediately.

If the FSCM is disabled and the system clock has not

started, the device will be in a frozen state at the Reset

vector until the system clock starts. From the user’s

perspective, the device will appear to be in Reset until

a system clock is available.

21.3.2

BOR: PROGRAMMABLE

BROWN-OUT RESET

The BOR (Brown-out Reset) module is based on an

internal voltage reference circuit. The main purpose of

the BOR module is to generate a device Reset when a

brown-out condition occurs. Brown-out conditions are

generally caused by glitches on the AC mains (i.e.,

missing portions of the AC cycle waveform due to bad

power transmission lines or voltage sags due to exces-

sive current draw when a large inductive load is turned

on).

The BOR module allows selection of one of the

following voltage trip points:

•2.6V–2.71V

•4.1V–4.4V

• 4.58V–4.73V

A BOR will generate a Reset pulse which will reset the

device. The BOR will select the clock source, based on

the device Configuration bit values (FOS<2:0> and

FPR<4:0>). Furthermore, if an oscillator mode is

selected, the BOR will activate the Oscillator Start-up

Timer (OST). The system clock is held until OST

expires. If the PLL is used, then the clock will be held

until the LOCK bit (OSCCON<5>) is ‘1’.

VDD

MCLR

Internal POR

PWRT Time-out

OST Time-out

Internal Reset

TPWRT

TOST

Note:

The BOR voltage trip points indicated here

are nominal values provided for design

guidance only.

DSPIC30F0010AT-20E/S Datasheet(PDF) 157 Page - Microchip Technology

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