16F1825 datasheet(57/420 Pages) MICROCHIP

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Preliminary

DS41440A-page 57

PIC16F/LF1825/1829

5.0

OSCILLATOR MODULE (WITH

FAIL-SAFE CLOCK MONITOR)

5.1

Overview

The oscillator module has a wide variety of clock

sources and selection features that allow it to be used

in a wide range of applications while maximizing perfor-

mance and minimizing power consumption. Figure 5-1

illustrates a block diagram of the oscillator module.

Clock sources can be supplied from external oscillators,

quartz crystal resonators, ceramic resonators and

Resistor-Capacitor (RC) circuits. In addition, the system

clock source can be supplied from one of two internal

oscillators and PLL circuits, with a choice of speeds

selectable via software. Additional clock features

include:

• Selectable system clock source between external

or internal sources via software.

• Two-Speed Start-up mode, which minimizes

latency between external oscillator start-up and

code execution.

• Fail-Safe Clock Monitor (FSCM) designed to

detect a failure of the external clock source (LP,

XT, HS, EC or RC modes) and switch

automatically to the internal oscillator.

• Oscillator Start-up Timer (OST) ensures stability

of crystal oscillator sources

The oscillator module can be configured in one of eight

clock modes.

ECL – External Clock Low Power mode

(0 MHz to 0.5 MHz)

ECM – External Clock Medium Power mode

(0.5 MHz to 4 MHz)

ECH – External Clock High Power mode

(4 MHz to 32 MHz)

LP – 32 kHz Low-Power Crystal mode.

XT – Medium Gain Crystal or Ceramic Resonator

Oscillator mode (up to 4 MHz)

HS – High Gain Crystal or Ceramic Resonator

mode (4 MHz to 20 MHz)

RC – External Resistor-Capacitor (RC).

INTOSC – Internal oscillator (31 kHz to 32 MHz).

Clock Source modes are selected by the FOSC<2:0>

bits in the Configuration Word 1. The FOSC bits

determine the type of oscillator that will be used when

the device is first powered.

The EC clock mode relies on an external logic level

signal as the device clock source. The LP, XT and HS

clock modes require an external crystal or resonator to

be connected to the device. Each mode is optimized for

a different frequency range. The RC clock mode

requires an external resistor and capacitor to set the

oscillator frequency.

The INTOSC internal oscillator block produces low,

medium, and high frequency clock sources, designated

LFINTOSC, MFINTOSC, and HFINTOSC. (see

Internal Oscillator Block, Figure 5-1). A wide selection

of device clock frequencies may be derived from these

three clock sources.

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