PIC18F6520 datasheet(21/380 Pages) MICROCHIP

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DS39609C-page 21

PIC18F6520/8520/6620/8620/6720/8720

2.0

OSCILLATOR

CONFIGURATIONS

2.1

Oscillator Types

The PIC18FXX20 devices can be operated in eight

different oscillator modes. The user can program three

configuration bits (FOSC2, FOSC1 and FOSC0) to

select one of these eight modes:

Low-Power Crystal

Crystal/Resonator

High-Speed Crystal/Resonator

HS+PLL

High-Speed Crystal/Resonator

with PLL enabled

External Resistor/Capacitor

RCIO

External Resistor/Capacitor with

I/O pin enabled

External Clock

ECIO

External Clock with I/O pin

enabled

2.2

Crystal Oscillator/Ceramic

Resonators

In XT, LP, HS or HS+PLL Oscillator modes, a crystal or

ceramic resonator is connected to the OSC1 and

OSC2 pins to establish oscillation. Figure 2-1 shows

the pin connections.

The PIC18FXX20 oscillator design requires the use of

a parallel cut crystal.

FIGURE 2-1:

CRYSTAL/CERAMIC

RESONATOR OPERATION

(HS, XT OR LP

CONFIGURATION)

TABLE 2-1:

CAPACITOR SELECTION FOR

CERAMIC RESONATORS

Note:

Use of a series cut crystal may give a fre-

quency out of the crystal manufacturer’s

specifications.

Note 1:

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

values of C1 and C2.

A series resistor (RS) may be required for AT

strip cut crystals.

RF varies with the oscillator mode chosen.

C1(1)

C2(1)

XTAL

OSC2

OSC1

(3)

Sleep

Logic

PIC18FXX20

RS(2)

Internal

Ranges Tested:

Mode

Freq

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 following this table.

Resonators Used:

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%

16.0 MHz Murata Erie CSA16.00MX

 0.5%

All resonators used did not have built-in capacitors.

Note 1: Higher capacitance increases the stability

of the oscillator, but also increases the

start-up time.

2: When operating below 3V VDD, or when

using certain ceramic resonators at any

voltage, it may be necessary to use high

gain HS mode, try a lower frequency

resonator, or switch to a crystal oscillator.

3: Since each resonator/crystal has its own

characteristics, the user should consult

the resonator/crystal manufacturer for

appropriate

values

external

components,

verify

oscillator

performance.

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