PIC12F635ESS datasheet(37/234 Pages) MICROCHIP

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DS41232D-page 35

PIC12F635/PIC16F636/639

3.0

OSCILLATOR MODULE (WITH

FAIL-SAFE CLOCK MONITOR)

3.1

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 3-1

illustrates a block diagram of the Oscillator module.

Clock sources can be configured from external

oscillators, quartz crystal resonators, ceramic resonators

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

system clock source can be configured from one of two

internal oscillators, with a choice of speeds selectable via

software. Additional clock features include:

• Selectable system clock source between external

or internal 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.

The Oscillator module can be configured in one of eight

clock modes.

EC – External clock with I/O on OSC2/CLKOUT.

LP – 32 kHz Low-Power Crystal mode.

–

Medium

Gain

Crystal

Ceramic

Resonator Oscillator mode.

HS – High Gain Crystal or Ceramic Resonator

mode.

RC – External Resistor-Capacitor (RC) with

FOSC/4 output on OSC2/CLKOUT.

RCIO – External Resistor-Capacitor (RC) with

I/O on OSC2/CLKOUT.

INTOSC – Internal oscillator with FOSC/4 output

on OSC2 and I/O on OSC1/CLKIN.

INTOSCIO – Internal oscillator with I/O on

OSC1/CLKIN and OSC2/CLKOUT.

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

bits in the Configuration Word register (CONFIG). The

internal clock can be generated from two internal

oscillators.

The

HFINTOSC

calibrated

high-frequency

oscillator.

The

LFINTOSC

uncalibrated low-frequency oscillator.

FIGURE 3-1:

PIC® MCU CLOCK SOURCE BLOCK DIAGRAM

(CPU and Peripherals)

OSC1

OSC2

Sleep

External Oscillator

LP, XT, HS, RC, RCIO, EC

System Clock

8 MHz

4 MHz

2 MHz

1 MHz

500 kHz

125 kHz

250 kHz

IRCF<2:0>

111

110

101

100

011

010

001

000

31 kHz

Power-up Timer (PWRT)

FOSC<2:0>

(Configuration Word Register)

SCS<0>

(OSCCON Register)

Internal Oscillator

(OSCCON Register)

Watchdog Timer (WDT)

Fail-Safe Clock Monitor (FSCM)

HFINTOSC

8 MHz

LFINTOSC

31 kHz

INTOSC

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