PIC18F2480/2580/4480/4580
FIGURE 3-1:
CRYSTAL/CERAMIC
RESONATOROPERATION
(XT, LP, HS OR HSPLL
CONFIGURATION)
3.0
3.1
OSCILLATOR
CONFIGURATIONS
Oscillator Types
(1)
C1
OSC1
PIC18F2480/2580/4480/4580 devices can be operated
in ten different oscillator modes. The user can program
the Configuration bits, FOSC<3:0>, in Configuration
Register 1H to select one of these ten modes:
To
Internal
Logic
(3)
RF
XTAL
1. LP
2. XT
3. HS
Low-Power Crystal
Sleep
(2)
RS
Crystal/Resonator
(1)
PIC18FXXXX
C2
OSC2
High-Speed Crystal/Resonator
Note 1: See Table 3-1 and Table 3-2 for initial values of
C1 and C2.
4. HSPLL High-Speed Crystal/Resonator
with PLL Enabled
2: A series resistor (RS) may be required for AT
strip cut crystals.
5. RC
External Resistor/Capacitor with
FOSC/4 Output on RA6
3: RF varies with the oscillator mode chosen.
6. RCIO
External Resistor/Capacitor with I/O
on RA6
7. INTIO1 Internal Oscillator with FOSC/4 Output
on RA6 and I/O on RA7
TABLE 3-1:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
8. INTIO2 Internal Oscillator with I/O on RA6
and RA7
Typical Capacitor Values Used:
9. EC
External Clock with FOSC/4 Output
External Clock with I/O on RA6
Mode
Freq
OSC1
OSC2
10. ECIO
XT
455 kHz
2.0 MHz
4.0 MHz
56 pF
47 pF
33 pF
56 pF
47 pF
33 pF
3.2
Crystal Oscillator/Ceramic
Resonators
HS
8.0 MHz
16.0 MHz
27 pF
22 pF
27 pF
22 pF
In XT, LP, HS or HSPLL Oscillator modes, a crystal or
ceramic resonator is connected to the OSC1 and
OSC2 pins to establish oscillation. Figure 3-1 shows
the pin connections.
Capacitor values are for design guidance only.
These capacitors were tested with the resonators
listed below for basic start-up and operation. These
values are not optimized.
The oscillator design requires the use of a parallel
resonant crystal.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
VDD and temperature range for the application.
Note:
Use of a series resonant crystal may give
frequency out of the crystal
manufacturer’s specifications.
a
See the notes on page 30 for additional information.
Resonators Used:
455 kHz
2.0 MHz
4.0 MHz
8.0 MHz
16.0 MHz
Note:
When using resonators with frequencies
above 3.5 MHz, the use of HS mode,
rather than XT mode, is recommended.
HS mode may be used at any VDD for
which the controller is rated. If HS is
selected, it is possible that the gain of the
oscillator will overdrive the resonator.
Therefore, a series resistor should be
placed between the OSC2 pin and the
resonator. As a good starting point, the
recommended value of RS is 330Ω.
© 2009 Microchip Technology Inc.
DS39637D-page 29
MICROCHIP [ MICROCHIP ]
