Datasheet

 2003-2013 Microchip Technology Inc. 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:
1. LP Low-Power Crystal
2. XT Crystal/Resonator
3. HS High-Speed Crystal/Resonator
4. RC External Resistor/Capacitor
5. EC External Clock
6. ECIO External Clock with I/O pin
enabled
7. HS+PLL High-Speed Crystal/Resonator
with PLL enabled
8. RCIO External Resistor/Capacitor with
I/O pin enabled
9. 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 C1 C2
XT 455 kHz
2.0 MHz
4.0 MHz
68-100 pF
15-68 pF
15-68 pF
68-100 pF
15-68 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:
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 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.
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.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
Sleep
To
Logic
PIC18F6X2X/8X2X
RS
(2)
Internal