12C508 datasheet(36/113 Pages) MICROCHIP

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PIC12C5XX

DS40139E-page 36

8.2

Oscillator Configurations

8.2.1

OSCILLATOR TYPES

The PIC12C5XX can be operated in four different

oscillator

modes.

The

user

can

program

two

configuration bits (FOSC1:FOSC0) to select one of

these four modes:

•LP:

Low Power Crystal

• XT:

Crystal/Resonator

• INTRC: Internal 4 MHz Oscillator

• EXTRC: External Resistor/Capacitor

8.2.2

CRYSTAL OSCILLATOR / CERAMIC

RESONATORS

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

connected to the GP5/OSC1/CLKIN and GP4/OSC2

pins

establish

oscillation

(Figure 8-2).

The

PIC12C5XX oscillator design requires the use of a

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

frequency

out

the

crystal

manufacturers

specifications. When in XT or LP modes, the device

can have an external clock source drive the GP5/

OSC1/CLKIN pin (Figure 8-3).

FIGURE 8-2:

CRYSTAL OPERATION (OR

CERAMIC RESONATOR) (XT

OR LP OSC

CONFIGURATION)

FIGURE 8-3:

EXTERNAL CLOCK INPUT

OPERATION (XT OR LP OSC

CONFIGURATION)

Note 1: See Capacitor Selection tables for

recommended values of C1 and C2.

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

AT strip cut crystals.

3: RF approximate value = 10 M

Ω.

C1(1)

C2(1)

XTAL

OSC2

OSC1

RF(3)

SLEEP

To internal

logic

RS(2)

PIC12C5XX

Clock from

ext. system

OSC1

OSC2

Open

PIC12C5XX

TABLE 8-1:

CAPACITOR SELECTION

FOR CERAMIC RESONATORS

- PIC12C5XX

TABLE 8-2:

CAPACITOR SELECTION

FOR CRYSTAL OSCILLATOR -

PIC12C5XX

Osc

Type

Resonator

Freq

Cap. Range

4.0 MHz

30 pF

These values are for design guidance only. Since

each resonator has its own characteristics, the user

should consult the resonator manufacturer for

appropriate values of external components.

Osc

Type

Resonator

Freq

Cap.Range

Cap. Range

32 kHz(1)

15 pF

200 kHz

1 MHz

4 MHz

47-68 pF

15 pF

47-68 pF

15 pF

Note 1: For VDD > 4.5V, C1 = C2

≈ 30 pF is

recommended.

These values are for design guidance only. Rs may

be required to avoid overdriving crystals with low

drive level specification. Since each crystal has its

own characteristics, the user should consult the crys-

tal manufacturer for appropriate values of external

components.

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