PIC18F2455_09 Datasheet, PDF (27/438 Pages) Microchip Technology – 28/40/44-Pin,High-Performance,Enhanced Flash,USB Microcontrollers with nanoWatt Technology

PIC18F2455/2550/4455/4550
2.2.2
CRYSTAL OSCILLATOR/CERAMIC
RESONATORS
In HS, HSPLL, XT and XTPLL Oscillator modes, a
crystal or ceramic resonator is connected to the OSC1
and OSC2 pins to establish oscillation. Figure 2-2
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 fre-
quency out of the crystal manufacturer’s
specifications.
FIGURE 2-2:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(XT, HS OR HSPLL
CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
RF⁽³⁾
To
Internal
Logic
RS⁽²⁾
C2⁽¹⁾
OSC2
Sleep
PIC18FXXXX
Note 1:
2:
3:
See Table 2-1 and Table 2-2 for initial values of
C1 and C2.
A series resistor (RS) may be required for AT
strip cut crystals.
RF varies with the oscillator mode chosen.
TABLE 2-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Typical Capacitor Values Used:
Mode
Freq
OSC1
OSC2
XT
4.0 MHz
33 pF
33 pF
HS
8.0 MHz
16.0 MHz
27 pF
22 pF
27 pF
22 pF
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.
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.
Resonators Used:
4.0 MHz
8.0 MHz
16.0 MHz
When using ceramic resonators with frequencies
above 3.5 MHz, HS mode is recommended over XT
mode. HS mode may be used at any VDD for which
the controller is rated. If HS is selected, the gain of the
oscillator may 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 330 Ω.
© 2009 Microchip Technology Inc.
DS39632E-page 25