Datasheet
© 2007 Microchip Technology Inc. DS39599G-page 19
PIC18F2220/2320/4220/4320
2.0 OSCILLATOR
CONFIGURATIONS
2.1 Oscillator Types
The PIC18F2X20 and PIC18F4X20 devices can be
operated in ten different oscillator modes. The user can
program the Configuration bits, FOSC3:FOSC0, in
Configuration Register 1H to select one of these ten
modes:
1. LP Low-Power Crystal
2. XT Crystal/Resonator
3. HS High-Speed Crystal/Resonator
4. HSPLL High-Speed Crystal/Resonator
with PLL Enabled
5. RC External Resistor/Capacitor with
F
OSC/4 Output on RA6
6. RCIO External Resistor/Capacitor with
I/O on RA6
7. INTIO1 Internal Oscillator with F
OSC/4
Output on RA6 and I/O on RA7
8. INTIO2 Internal Oscillator with I/O on RA6
and RA7
9. EC External Clock with F
OSC/4 Output
10. ECIO External Clock with I/O on RA6
2.2 Crystal Oscillator/Ceramic
Resonators
In XT, LP, HS or HSPLL 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 oscillator design requires the use of a parallel cut
crystal.
FIGURE 2-1: CRYSTAL/CERAMIC
RESONATOR OPERATION
(XT, LP, HS OR HSPLL
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.
Typical Capacitor Values Used:
Mode Freq OSC1 OSC2
XT 455 kHz
2.0 MHz
4.0 MHz
56 pF
47 pF
33 pF
56 pF
47 pF
33 pF
HS 8.0 MHz
16.0 MHz
27 pF
22 pF
27 pF
22 pF
Capacitor values are for design guidance only.
These capacitors were tested with the resonators
listed below for basic start-up and operation. These
values are not optimized.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
V
DD and temperature range for the application.
See the notes on page 20 for additional information.
Resonators Used:
455 kHz 4.0 MHz
2.0 MHz 8.0 MHz
16.0 MHz
Note 1: See Table 2-1 and Table 2-2 for initial 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.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
Sleep
To
Logic
PIC18FXXXX
RS
(2)
Internal