
2004 Microchip Technology Inc.
DS30491C-page 23
PIC18F6585/8585/6680/8680
2.0
OSCILLATOR
CONFIGURATIONS
2.1
Oscillator Types
The PIC18F6585/8585/6680/8680 devices can be
operated in eleven different oscillator modes. The user
can program four configuration bits (FOSC3, FOSC2,
FOSC1 and FOSC0) to select one of these eleven
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
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 2-1shows the pin connections.
The PIC18F6585/8585/6680/8680 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.
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:
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 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 1:
values of C1 and C2.
2:
A series resistor (RS) may be required for AT
strip cut crystals.
3:
RF varies with the oscillator mode chosen.
C1(1)
C2(1)
XTAL
OSC2
OSC1
RF
(3)
Sleep
To
Logic
PIC18FXX80/XX85
RS(2)
Internal