PIC18F2X1X Datasheet, PDF (25/380 Pages) Microchip Technology – 28/40/44-PIN FLASH MICROCONTROLLERS WITH 10-BIT A/D AND NANO WATT TECHNOLOGY

2.0 OSCILLATOR
CONFIGURATIONS
2.1 Oscillator Types
PIC18F2X1X/4X1X devices can be operated in ten
different oscillator modes. The user can program the
configuration bits, FOSC3:FOSC0, in Configuration
Register 1H to select one of these ten modes:
1. LP
Low-Power Crystal
2. XT
Crystal/Resonator
3. HS
High-Speed Crystal/Resonator
4. HSPLL High-Speed Crystal/Resonator
with PLL enabled
5. RC
External Resistor/Capacitor with
FOSC/4 output on RA6
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
8. INTIO2 Internal Oscillator with I/O on RA6
and RA7
9. EC
External Clock with FOSC/4 output
10. ECIO External Clock with I/O on RA6
2.2 Crystal Oscillator/Ceramic
Resonators
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 2-1 shows
the pin connections.
The 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 manufacturer’s
specifications.
PIC18F2X1X/4X1X
FIGURE 2-1:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(XT, LP, HS OR HSPLL
CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
RF⁽³⁾
To
Internal
Logic
RS⁽²⁾
C2⁽¹⁾
OSC2
Sleep
PIC18FXXXX
Note 1: See Table 2-1 and Table 2-2 for initial 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.
TABLE 2-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Typical Capacitor Values Used:
Mode
Freq
OSC1
OSC2
XT
3.58 MHz
4.19 MHz
4 MHz
4 MHz
15 pF
15 pF
30 pF
50 pF
15 pF
15 pF
30 pF
50 pF
Capacitor values are for design guidance only.
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.
See the notes following Table 2-2 for additional
information.
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.
 2004 Microchip Technology Inc.
Preliminary
DS39636A-page 23