PIC18F6525 datasheet(21/400 Pages) MICROCHIP

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DS39612C-page 21

PIC18F6525/6621/8525/8621

2.0

OSCILLATOR

CONFIGURATIONS

2.1

Oscillator Types

The PIC18F6525/6621/8525/8621 devices can be

operated in twelve different oscillator modes. The user

can program four configuration bits (FOSC3, FOSC2,

FOSC1 and FOSC0) to select one of these eight

modes:

Low-Power Crystal

Crystal/Resonator

High-Speed Crystal/Resonator

External Resistor/Capacitor

External Clock

ECIO

External Clock with I/O pin

enabled

HS+PLL

High-Speed Crystal/Resonator

with PLL enabled

RCIO

External Resistor/Capacitor with

I/O pin enabled

ECIO+SPLL External Clock with software

controlled PLL

10. ECIO+PLL

External Clock with PLL and I/O

pin enabled

11. HS+SPLL

High-Speed Crystal/Resonator

with software control

12. RCIO

External Resistor/Capacitor with

I/O pin enabled

2.2

Crystal Oscillator/Ceramic

Resonators

In XT, LP, HS, HS+PLL or HS+SPLL 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 PIC18F6525/6621/8525/8621 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

frequency out of the crystal manufacturers

specifications.

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 kHz

8 MHz

4 MHz

16 MHz

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.

Note

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

PIC18F6X2X/8X2X

RS(2)

Internal

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