PIC18F44J50-I Datasheet, PDF (37/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
3.2.2
CRYSTAL OSCILLATOR/CERAMIC
RESONATORS
In HS and HSPLL Oscillator modes, a crystal or
ceramic resonator is connected to the OSC1 and
OSC2 pins to establish oscillation. Figure 3-2 displays
the pin connections.
The oscillator design requires the use of a parallel
resonant crystal.
Note:
Use of a series resonant crystal may give a
frequency out of the crystal manufacturer’s
specifications.
FIGURE 3-2:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS OR HSPLL
CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
RF
To
Internal
Logic
RS⁽²⁾
C2⁽¹⁾
OSC2
Sleep
PIC18F46J50
Note 1: See Table 3-2 and Table 3-3 for initial values
of C1 and C2.
2: A series resistor (RS) may be required to
avoid overdriving crystals with low drive level
specification.
TABLE 3-2: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Typical Capacitor Values Used:
Mode
Freq
OSC1
OSC2
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 3-3 for additional
information.
Resonators Used:
4.0 MHz
8.0 MHz
16.0 MHz
TABLE 3-3: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
HS
Crystal
Freq
4 MHz
8 MHz
16 MHz
Typical Capacitor Values
Tested:
C1
27 pF
22 pF
18 pF
C2
27 pF
22 pF
18 pF
Capacitor values are for design guidance only.
These capacitors were tested with the crystals 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 this table for additional
information.
Crystals Used:
4 MHz
8 MHz
16 MHz
Note 1: Higher capacitance not only increases
the stability of the oscillator, but also
increases the start-up time.
2: Since each resonator/crystal has its own
characteristics, the user should consult
the resonator/crystal manufacturer for
appropriate values of external
components.
3: Rs may be required to avoid overdriving
crystals with a low drive level specification.
4: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
An internal postscaler allows users to select a clock
frequency other than that of the crystal or resonator.
Frequency division is determined by the CPDIV
Configuration bits. Users may select a clock frequency
of the oscillator frequency, or 1/2, 1/3 or 1/6 of the
frequency.
 2011 Microchip Technology Inc.
DS39931D-page 37