Datasheet

 2010 Microchip Technology Inc. Preliminary DS39979A-page 29
PIC18F87J72 FAMILY
3.4 External Oscillator Modes
3.4.1 CRYSTAL OSCILLATOR/CERAMIC
RESONATORS (HS MODES)
In HS or HSPLL Oscillator modes, a crystal or ceramic
resonator is connected to the OSC1 and OSC2 pins to
establish oscillation. Figure 3-2 shows the pin
connections.
The oscillator design requires the use of a crystal rated
for parallel resonant operation.
TABLE 3-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
TABLE 3-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
FIGURE 3-2: CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS OR HSPLL
CONFIGURATION)
Note: Use of a crystal rated for series resonant
operation may give a frequency out of the
crystal manufacturer’s specifications.
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.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
V
DD and temperature range for the application. Refer
to the following application notes for oscillator specific
information:
• AN588, “PIC
®
Microcontroller Oscillator Design
Guide”
• AN826, “Crystal Oscillator Basics and Crystal
Selection for rfPIC
®
and PIC
®
Devices”
• AN849, “Basic PIC
®
Oscillator Design”
• AN943, “Practical PIC
®
Oscillator Analysis and
Design”
• AN949, “Making Your Oscillator Work”
See the notes following Table 3-2 for additional
information.
Osc Type
Crystal
Freq.
Typical Capacitor Values
Tested:
C1 C2
HS 4 MHz 27 pF 27 pF
8 MHz 22 pF 22 pF
20 MHz 15 pF 15 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
V
DD and temperature range for the application.
Refer to the Microchip application notes cited in
Table 3-1 for oscillator specific information. Also see
the notes following this table for additional
information.
Note 1: Higher capacitance increases the stability
of 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 low drive level specification.
4: Always verify oscillator performance over
the V
DD and temperature range that is
expected for the application.
Note 1: See Table 3-1 and Table 3-2 for initial values of
C1 and C2.
2: A series resistor (R
S) may be required for AT
strip cut crystals.
3: R
F varies with the oscillator mode chosen.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
Sleep
To
Logic
RS
(2)
Internal
PIC18F87J72