PIC16LC712 datasheet(53/106 Pages) MICROCHIP

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DS41106C-page 53

PIC16C712/716

9.2

Oscillator Configurations

9.2.1

OSCILLATOR TYPES

The PIC16CXXX can be operated in four different

Oscillator

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

9.2.2

CRYSTAL OSCILLATOR/CERAMIC

RESONATORS

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

is connected to the OSC1/CLKIN and OSC2/CLKOUT

pins

establish

oscillation

(Figure 9-2).

The

PIC16CXXX oscillator design requires the use of a par-

allel cut crystal. Use of a series cut crystal may give a

frequency out of the crystal manufacturers specifica-

tions. When in XT, LP or HS modes, the device can

have an external clock source to drive the OSC1/

CLKIN pin (Figure 9-3).

FIGURE 9-2:

CRYSTAL/CERAMIC

RESONATOR OPERATION

(HS, XT OR LP

OSC CONFIGURATION)

FIGURE 9-3:

EXTERNAL CLOCK INPUT

OPERATION (HS, XT OR

LP OSC

CONFIGURATION)

TABLE 9-1:

CERAMIC RESONATORS

TABLE 9-2:

CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

Note 1: See

Table 9-1

and

Table 9-2

for

recommended 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

PIC16C7XX

RS(2)

internal

OSC1

OSC2

Open

Clock from

ext. system

PIC16C7XX

Ranges Tested:

Mode

Freq

OSC1

OSC2

455 kHz

2.0 MHz

4.0 MHz

68-100 pF

15-68 pF

68-100 pF

15-68 pF

8.0 MHz

16.0 MHz

10-68 pF

10-22 pF

10-68 pF

10-22 pF

These values are for design guidance only. See

notes at bottom of page.

Osc Type

Crystal

Freq

Cap. Range

32 kHz

33 pF

200 kHz

15 pF

200 kHz

47-68 pF

1 MHz

15 pF

4 MHz

15 pF

4 MHz

15 pF

8 MHz

15-33 pF

20 MHz

15-33 pF

These values are for design guidance only. See

notes at bottom of page.

Note 1:

Recommended values of C1 and C2 are

identical to the ranges tested (Table 9-1).

Higher capacitance increases the stability

of the oscillator, but also increases the

start-up time.

Since each resonator/crystal has its own

characteristics, the user should consult

the resonator/crystal manufacturer for

appropriate values of external compo-

nents.

Rs may be required in HS mode, as well

as XT mode to avoid overdriving crystals

with low drive level specification.

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