PIC16F884-I/ML【PDF 3/16 页】IC PIC MCU FLASH 4KX14 44QFN

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Sheet目录3873

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2009 Microchip Technology Inc.

DS80302F-page 11

PIC16F88X

Module: LP/Timer1 Oscillator Operation

Below 25°C

1-2% of devices experience reduced drive as

temperatures approach -40°C. This will result in a

loss

Timer1

counts

stopped

Timer1

oscillation.

This can also prevent Timer1 oscillator start-up

under cold conditions.

Work around

Use of low-power crystals properly matched to the

device will reduce the likelyhood of failure. A 1m

resister between OSC2 and VDD will further

improve the drive strength of the circuit.

Affected Silicon Revisions

PIC16F882

PIC16F883/PIC16F884

PIC16F886/PIC16F887

10. Module: Timer0 and WDT Prescaler

Assignment Spurious Reset

A spurious Reset may occur if the Timer0/

Watchdog Timer (WDT) prescaler is assigned

from the WDT to Timer0 and then back to the

WDT.

Summary

The issue only arises when all of the below

conditions are met:

Timer0 external clock input (TOCKI) is enabled.

The Prescaler is assigned to the WDT, then to

the Timer0 and back to the WDT.

During the assignments, the T0CKI pin is high

when bit TOSE is set, or low when TOSE is

clear.

The 1:1 Prescaler option is chosen.

Description

On a POR, the Timer0/WDT prescaler is assigned

to the WDT.

If the prescaler is reassigned to Timer0 and

Timer0 external clock input (TOCKI) is enabled

then the prescaler would be clocked by a transition

on the TOCKI pin.

On power-up, the TOCKI pin is (by default)

enabled for Timer0 in the OPTION register.

If the T0CKI pin is:

High and Timer0 is configured to transition on a

falling edge (TOSE set), or

Low and Timer0 is configured to transition on a

rising edge (TOSE clear)

Then, if the prescaler is reassigned to the WDT, a

clock pulse to the prescaler will be generated on

the reassignment.

If the prescaler is configured for the 1:1 option, the

clock pulse will incorrectly cause a WDT Time-out

Reset of the device.

Work around

Disable the Timer0 external clock input by

clearing the TOCKI bit in the OPTION

Modify the TOSE bit in the OPTION register to

the opposite configuration for the logic level

on the T0CKI pin.

Select a prescaler rate other than 1:1 and

issue a CLRWDT instruction before switching

to the final prescaler rate.

Affected Silicon Revisions

PIC16F882

PIC16F883/PIC16F884

PIC16F886/PIC16F887

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