PIC18FXX20
2.0
2.1
OSCILLATOR
CONFIGURATIONS
Oscillator Types
TABLE 2-1:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Ranges Tested:
The PIC18FXX20 devices can be operated in eight dif-
ferent Oscillator modes. The user can program three
configuration bits (FOSC2, FOSC1, and FOSC0) to
select one of these eight modes:
1.
2.
3.
4.
5.
6.
7.
8.
LP
XT
HS
HS+PLL
RC
RCIO
EC
ECIO
Low Power Crystal
Crystal/Resonator
High Speed Crystal/Resonator
High Speed Crystal/Resonator
with PLL enabled
External Resistor/Capacitor
External Resistor/Capacitor with
I/O pin enabled
External Clock
External Clock with I/O pin
enabled
Mode
XT
Freq
C1
C2
455 kHz
68 - 100 pF 68 - 100 pF
2.0 MHz
15 - 68 pF
15 - 68 pF
4.0 MHz
15 - 68 pF
15 - 68 pF
HS
8.0 MHz
10 - 68 pF
10 - 68 pF
16.0 MHz
10 - 22 pF
10 - 22 pF
These values are for design guidance only.
See notes following this table.
Resonators Used:
455 kHz Panasonic EFO-A455K04B
±
0.3%
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.
2.2
Crystal Oscillator/Ceramic
Resonators
In XT, LP, HS or HS+PLL 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 PIC18FXX20 oscillator design requires the use of
a parallel cut crystal.
Note:
Use of a series cut crystal may give a fre-
quency out of the crystal manufacturer’s
specifications.
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.
FIGURE 2-1:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP
CONFIGURATION)
OSC1
To
Internal
Logic
SLEEP
C1
(1)
XTAL
R
S
(2)
C2
(1)
OSC2
R
F
(3)
PIC18FXX20
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.
2003 Microchip Technology Inc.
Advance Information
DS39609A-page 21
MICROCHIP [ MICROCHIP TECHNOLOGY ]
