PIC18F6525/6621/8525/8621
FIGURE 2-1:
CRYSTAL/CERAMIC
RESONATOROPERATION
(HS, XT OR LP
2.0
2.1
OSCILLATOR
CONFIGURATIONS
CONFIGURATION)
Oscillator Types
(1)
C1
OSC1
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:
To
Internal
Logic
(3)
RF
XTAL
Sleep
(2)
RS
1. LP
2. XT
3. HS
4. RC
5. EC
6. ECIO
Low-Power Crystal
(1)
C2
PIC18F6X2X/8X2X
Crystal/Resonator
OSC2
High-Speed Crystal/Resonator
External Resistor/Capacitor
External Clock
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.
External Clock with I/O pin
enabled
3: RF varies with the oscillator mode chosen.
7. HS+PLL
8. RCIO
High-Speed Crystal/Resonator
with PLL enabled
External Resistor/Capacitor with
I/O pin enabled
TABLE 2-1:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
9. ECIO+SPLL External Clock with software
controlled PLL
Ranges Tested:
10. ECIO+PLL External Clock with PLL and I/O
pin enabled
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
11. HS+SPLL
High-Speed Crystal/Resonator
with software control
12. RCIO
External Resistor/Capacitor with
I/O pin enabled
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.
2.2
Crystal Oscillator/Ceramic
Resonators
Resonators Used:
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.
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.
The PIC18F6525/6621/8525/8621 oscillator design
requires the use of a parallel cut crystal.
Note:
Use of a series cut crystal may give a
frequency out of the crystal manufacturers
specifications.
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.
2005 Microchip Technology Inc.
DS39612B-page 21
MICROCHIP [ MICROCHIP ]
