PIC16F84 datasheet(40/128 Pages) MICROCHIP

40 / 128 page

PIC16F8X

DS30430D-page 40

 1996-2013 Microchip Technology Inc.

FIGURE 8-4:

EXTERNAL CLOCK INPUT

OPERATION (HS, XT OR LP

OSC CONFIGURATION)

TABLE 8-1

CAPACITOR SELECTION FOR

CERAMIC RESONATORS

TABLE 8-2

CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

8.2.3

EXTERNAL CRYSTAL OSCILLATOR

CIRCUIT

Either a prepackaged oscillator can be used or a simple

oscillator

circuit

with

TTL

gates

can

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 are

available; one with series resonance, and one with

parallel resonance.

Figure 8-5 shows a parallel resonant oscillator circuit.

The circuit is designed to use the fundamental

frequency of the crystal. The 74AS04 inverter performs

the 180-degree phase shift that a parallel oscillator

requires.

The

4.7 k

 resistor provides negative

feedback for stability. The 10 k

 potentiometer biases

the 74AS04 in the linear region. This could be used for

external oscillator designs.

FIGURE 8-5:

EXTERNAL PARALLEL

RESONANT CRYSTAL

OSCILLATOR CIRCUIT

Figure 8-6 shows a series resonant oscillator circuit.

This circuit is also designed to use the fundamental

frequency of the crystal. The inverter performs a

180-degree phase shift. The 330 k

 resistors provide

the negative feedback to bias the inverters in their

linear region.

Ranges Tested:

Mode

Freq

OSC1/C1

OSC2/C2

455 kHz

2.0 MHz

4.0 MHz

47 - 100 pF

15 - 33 pF

47 - 100 pF

15 - 33 pF

8.0 MHz

10.0 MHz

15 - 33 pF

Note :

Recommended values of C1 and C2 are identical to

the ranges tested table.

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 manufacturer for the

appropriate values of external components.

Resonators Tested:

455 kHz

Panasonic EFO-A455K04B

0.3%

2.0 MHz

Murata Erie CSA2.00MG

0.5%

4.0 MHz

Murata Erie CSA4.00MG

0.5%

8.0 MHz

Murata Erie CSA8.00MT

 0.5%

10.0 MHz

Murata Erie CSA10.00MTZ

0.5%

None of the resonators had built-in capacitors.

Mode

Freq

OSC1/C1

OSC2/C2

32 kHz

200 kHz

68 - 100 pF

15 - 33 pF

68 - 100 pF

15 - 33 pF

100 kHz

2 MHz

4 MHz

100 - 150 pF

15 - 33 pF

100 - 150 pF

15 - 33 pF

4 MHz

10 MHz

15 - 33 pF

Note :

Higher capacitance increases the stability of

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 speci-

fication. Since each crystal has its own characteris-

tics, the user should consult the crystal

manufacturer for appropriate values of external

components.

For VDD > 4.5V, C1 = C2

 30 pF is recommended.

OSC1

OSC2

Open

Clock from

ext. system

PIC16FXX

Crystals Tested:

32.768 kHz

Epson C-001R32.768K-A

 20 PPM

100 kHz

Epson C-2 100.00 KC-P

 20 PPM

200 kHz

STD XTL 200.000 KHz

 20 PPM

1.0 MHz

ECS ECS-10-13-2

 50 PPM

2.0 MHz

ECS ECS-20-S-2

 50 PPM

4.0 MHz

ECS ECS-40-S-4

 50 PPM

10.0 MHz

ECS ECS-100-S-4

 50 PPM

20 pF

+5V

20 pF

10k

4.7k

10k

74AS04

XTAL

10k

74AS04

PIC16FXX

CLKIN

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