PIC18F6520/8520/6620/8620/6720/8720
2.0
2.1
OSCILLATOR
CONFIGURATIONS
Oscillator Types
TABLE 2-1:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Ranges Tested:
Freq
C1
C2
Mode
XT
The PIC18FXX20 devices can be operated in eight
different 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
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:
2.0 MHz Murata Erie CSA2.00MG
卤
0.5%
4.0 MHz Murata Erie CSA4.00MG
卤
0.5%
8.0 MHz Murata Erie CSA8.00MT
卤
0.5%
16.0 MHz Murata Erie CSA16.00MX
卤
0.5%
All resonators used did not have built-in capacitors.
2.2
Crystal Oscillator/Ceramic
Resonators
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
appropriate
values
of
external
components,
or
verify
oscillator
performance.
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鈥檚
specifications.
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:
2:
3:
See Table 2-1 and Table 2-2 for recommended
values of C1 and C2.
A series resistor (R
S
) may be required for AT
strip cut crystals.
R
F
varies with the oscillator mode chosen.
铮?/div>
2004 Microchip Technology Inc.
DS39609B-page 21
prev
next