PIC1F628 datasheet(95/170 Pages) MICROCHIP

95 / 170 page

 2003 Microchip Technology Inc.

Preliminary

DS40300C-page 93

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 14-1). 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 14-4).

FIGURE 14-1:

CRYSTAL OPERATION

(OR CERAMIC

RESONATOR) (HS, XT OR

LP OSC

CONFIGURATION)

TABLE 14-1:

CAPACITOR SELECTION FOR

CERAMIC RESONATORS

TABLE 14-2:

CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

14.2.3

EXTERNAL CRYSTAL OSCILLATOR

CIRCUIT

Either a prepackaged oscillator can be used, or a

simple oscillator circuit with TTL gates can be built.

Prepackaged oscillators provide a wide operating

range and better stability. A well-designed crystal

oscillator will provide good performance with TTL

gates. Two types of crystal oscillator circuits can be

used; one with series resonance, or one with parallel

resonance.

Figure 14-2

shows

implementation

parallel

resonant oscillator circuit. The circuit is designed to use

the fundamental frequency of the crystal. The 74AS04

inverter performs the 180

° phase shift that a parallel

oscillator requires. The 4.7 k

Ω resistor provides the

negative

feedback

for

stability.

The

10 k

Ω

potentiometers bias the 74AS04 in the linear region.

This could be used for external oscillator designs.

Note

A series resistor may be required for some crys-

tals.

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

values of C1 and C2.

XTAL

OSC2

OSC1

SLEEP

PIC16F62X

NOTE 1

FOSC

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

Note

Higher capacitance increases the stability of the oscilla-

tor 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 res-

onator manufacturer 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

Note

Higher capacitance increases the stability of the oscilla-

tor 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 manufacturer for appropriate values of external

components.

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