P12C508 datasheet(26/84 Pages) MICROCHIP

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PIC12C5XX

DS40139A-page 26

Advanced Information

7.2

Oscillator Conﬁgurations

7.2.1

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

7.2.2

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 7-2).

The

PIC12C5XX 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 or LP modes, the device

can have an external clock source drive the GP5/

OSC1/CLKIN pin (Figure 7-3).

FIGURE 7-2:

CRYSTAL OPERATION (OR

CERAMIC RESONATOR) (XT

OR LP OSC

CONFIGURATION)

FIGURE 7-3:

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 varies with the crystal chosen

(approx. 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

PIC12C5XX

Open

TABLE 7-1:

CAPACITOR SELECTION

FOR CERAMIC RESONATORS

- PIC12C5XX

TABLE 7-2:

CAPACITOR SELECTION

FOR CRYSTAL OSCILLATOR

- PIC12C5XX

Osc

Type

Resonator

Freq

Cap. Range

455 kHz

2.0 MHz

4.0 MHz

68-100 pF

15-33 pF

10-22 pF

68-100 pF

15-33 pF

10-22 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

100 kHz

200 kHz

455 kHz

1 MHz

2 MHz

4 MHz

15-30 pF

15 pF

200-300 pF

100-200 pF

15-100 pF

15-30 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 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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