PIC16 datasheet(47/418 Pages) MICROCHIP

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DS40001609C-page 47

PIC16(L)F1508/9

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, 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, ECH, ECM, ECL or EXTRC modes) and

switch automatically to the internal oscillator.

• Oscillator Start-up Timer (OST) ensures stability

of crystal oscillator sources

• Fast start-up oscillator allows internal circuits to

power-up and stabilize before switching to the 16

MHz HFINTOSC

The oscillator module can be configured in one of the

following 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 20 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)

EXTRC – External Resistor-Capacitor

INTOSC – Internal oscillator (31 kHz to 16 MHz)

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

bits in the Configuration Words. The FOSC bits

determine the type of oscillator that will be used when

the device is first powered.

The ECH, ECM, and ECL clock modes rely 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 EXTRC clock mode requires an external resistor

and capacitor to set the oscillator frequency.

The INTOSC internal oscillator block produces a low

and

high-frequency

clock

source,

designated

LFINTOSC and HFINTOSC. (See Internal Oscillator

Block, Figure 5-1). A wide selection of device clock

frequencies may be derived from these two clock

sources.

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