PIC16F72SLASHML datasheet(63/136 Pages) MICROCHIP

63 / 136 page

 2002 Microchip Technology Inc.

DS39597B-page 61

PIC16F72

11.2

Oscillator Configurations

11.2.1

OSCILLATOR TYPES

The PIC16F72 can be operated in four different Oscil-

lator modes. The user can program two configuration

bits (FOSC1 and FOSC0) to select one of these four

modes:

• LP

Low Power Crystal

• XT

Crystal/Resonator

• HS

High Speed Crystal/Resonator

• RC

Resistor/Capacitor

11.2.2

CRYSTAL OSCILLATOR/CERAMIC

RESONATORS

In XT, LP or HS modes, a crystal or ceramic resonator

is connected to the OSC1/CLKI and OSC2/CLKO pins

to establish oscillation (Figure 11-1). The PIC16F72

oscillator design requires the use of a parallel cut crys-

tal. Use of a series cut crystal may give a frequency out

of the crystal manufacturers specifications. When in HS

mode, the device can accept an external clock source

to drive the OSC1/CLKI pin (Figure 11-2). See

Figure 14-1 or Figure 14-2 (depending on the part

number and VDD range) for valid external clock

frequencies.

FIGURE 11-1:

CRYSTAL/CERAMIC

RESONATOR OPERATION

(HS, XT OR LP

OSC CONFIGURATION)

FIGURE 11-2:

EXTERNAL CLOCK INPUT

OPERATION (HS OSC

CONFIGURATION)

TABLE 11-1:

CERAMIC RESONATORS

(FOR DESIGN

GUIDANCE ONLY)

Note

1: See Table 11-1 and Table 11-2 for typical

values of C1 and C2.

2: A series resistor (RS) may be required for

AT strip cut crystals.

3: RF varies with the crystal chosen.

C1(1)

C2(1)

XTAL

OSC2

OSC1

RF(3)

SLEEP

logic

PIC16F72

RS(2)

internal

Typical Capacitor Values Used:

Mode

Freq

OSC1

OSC2

455 kHz

2.0 MHz

4.0 MHz

56 pF

47 pF

33 pF

56 pF

47 pF

33 pF

8.0 MHz

16.0 MHz

27 pF

22 pF

27 pF

22 pF

Capacitor values are for design guidance only.

These capacitors were tested with the resonators

listed below for basic start-up and operation. These

values were not optimized.

Different capacitor values may be required to produce

acceptable oscillator operation. The user should test

the performance of the oscillator over the expected

VDD and temperature range for the application.

See the notes at the bottom of page 62 for additional

information.

OSC1

OSC2

Open

Clock from

Ext. System

PIC16F72

(HS Mode)

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