PIC18F242 datasheet(19/332 Pages) MICROCHIP

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DS39564C-page 17

PIC18FXX2

2.0

OSCILLATOR

CONFIGURATIONS

2.1

Oscillator Types

The PIC18FXX2 can be operated in eight different

Oscillator modes. The user can program three configu-

ration 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

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 PIC18FXX2 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 manufacturers

specifications.

Note

1: See

Table 2-1

and

Table 2-2

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 Oscillator mode chosen.

C1(1)

C2(1)

XTAL

OSC2

OSC1

(3)

SLEEP

Logic

PIC18FXXX

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:

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%

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 appro-

priate values of external components, or

verify oscillator performance.

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