PIC16F628-20SLASHP datasheet(97/160 Pages) MICROCHIP

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Preliminary

DS40300B-page 97

PIC16F62X

14.2

Oscillator Configurations

14.2.1

OSCILLATOR TYPES

The PIC16F62X

can be operated in eight different

oscillator options. The user can program three

configuration bits (FOSC2 thru FOSC0) to select one of

these eight modes:

• LP

Low Power Crystal

• XT

Crystal/Resonator

• HS

High Speed Crystal/Resonator

• ER

External Resistor (2 modes)

• INTRC

Internal Resistor/Capacitor (2 modes)

• EC

External Clock In

14.2.2

CRYSTAL OSCILLATOR / CERAMIC

RESONATORS

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

is connected to the OSC1 and OSC2 pins to establish

oscillation (Figure 14-2). The PIC16F62X

oscillator

design requires the use of a parallel cut crystal. Use of

a series cut crystal may give a frequency out of the

crystal manufacturers specifications. When in XT, LP or

HS modes, the device can have an external clock

source to drive the OSC1 pin (Figure 14-3).

FIGURE 14-2: CRYSTAL OPERATION

(OR CERAMIC RESONATOR)

(HS, XT OR LP OSC

CONFIGURATION)

FIGURE 14-3: EXTERNAL CLOCK INPUT

OPERATION (HS, XT OR LP

OSC CONFIGURATION)

See Table 14-1 and Table 14-2 for recommended

values of C1 and C2.

Note:

A series resistor may be required for

AT strip cut crystals.

XTAL

OSC2

OSC1

SLEEP

To internal logic

PIC16F62X

see Note

Clock from

ext. system

PIC16F62X

OSC1

OSC2

Open

TABLE 14-1:

CAPACITOR SELECTION FOR

CERAMIC RESONATORS

TABLE 14-2:

CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

Ranges Characterized:

Mode

Freq

OSC1(C1)

OSC2(C2)

455 kHz

2.0 MHz

4.0 MHz

22 - 100 pF

15 - 68 pF

22 - 100 pF

15 - 68 pF

8.0 MHz

16.0 MHz

10 - 68 pF

10 - 22 pF

10 - 68 pF

10 - 22 pF

Higher capacitance increases the stability of the oscillator

but also increases the start-up time. These values are for

design guidance only. Since each resonator has its own

characteristics, the user should consult the resonator man-

ufacturer for appropriate values of external components.

Mode

Freq

OSC1(C1)

OSC2(C2)

32 kHz

200 kHz

68 - 100 pF

15 - 30 pF

68 - 100 pF

15 - 30 pF

100 kHz

2 MHz

4 MHz

68 - 150 pF

15 - 30 pF

150 - 200 pF

15 - 30 pF

8 MHz

10 MHz

20 MHz

15 - 30 pF

Higher capacitance increases the stability of the oscillator

but also increases the start-up time. These values are for

design guidance only. Rs may be required in HS mode as

well as XT mode to avoid overdriving crystals with low drive

level

specification. Since

each

crystal

has

its

own

characteristics, the user should consult the crystal manu-

facturer for appropriate values of external components.

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