Datasheet

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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:

1. LP Low Power Crystal

2. XT Crystal/Resonator

3. HS High Speed Crystal/Resonator

4. HS + PLL High Speed Crystal/Resonator

with PLL enabled

5. RC External Resistor/Capacitor

6. RCIO External Resistor/Capacitor with

I/O pin enabled

7. EC External Clock

8. 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 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 (R

S) may be required for

AT strip cut crystals.

3: R

F varies with the Oscillator mode chosen.

(1)

XTAL

OSC2

OSC1

(3)

SLEEP

Logic

PIC18FXXX

(2)

Internal

Ranges Tested:

Mode Freq C1 C2

XT 455 kHz

2.0 MHz

4.0 MHz

68 - 100 pF

15 - 68 pF

68 - 100 pF

15 - 68 pF

HS 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 V

DD, 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.