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PIC18F97J60 FAMILY
DS39762F-page 50
2011 Microchip Technology Inc.
3.3
Crystal Oscillator/Ceramic
Resonators (HS Modes)
In HS or HSPLL Oscillator modes, a crystal 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 that
is rated for parallel resonant operation.
FIGURE 3-2:
CRYSTAL OSCILLATOR
OPERATION (HS OR
HSPLL CONFIGURATION)
TABLE 3-1:
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
3.4
External Clock Input (EC Modes)
The EC and ECPLL Oscillator modes require an exter-
nal clock source to be connected to the OSC1 pin.
There is no oscillator start-up time required after a
Power-on Reset or after an exit from Sleep mode.
In the EC Oscillator mode, the oscillator frequency,
divided by 4, is available on the OSC2 pin. This signal
may be used for test purposes or to synchronize other
logic.
Figure 3-3 shows the pin connections for the EC
Oscillator mode.
FIGURE 3-3:
EXTERNAL CLOCK
INPUT OPERATION
(EC CONFIGURATION)
An external clock source may also be connected to the
OSC1 pin in the HS mode, as shown in
Figure 3-4. In
this configuration, the OSC2 pin is left open. Current
consumption in this configuration will be somewhat
higher than EC mode, as the internal oscillator’s
feedback circuitry will be enabled (in EC mode, the
feedback circuit is disabled).
FIGURE 3-4:
EXTERNAL CLOCK
INPUT OPERATION
(HS CONFIGURATION)
Note:
Use of a crystal rated for series resonant
operation may give a frequency out of the
crystal manufacturer’s specifications.
Osc Type
Crystal
Freq.
Typical Capacitor Values
Tested:
C1
C2
HS
25 MHz
33 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. 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 this table for additional
information.
Note 1:
See
Table 3-1 for initial values of C1 and C2.
2:
A series resistor (RS) may be required for
crystals with a low drive specification.
3:
RF varies with the oscillator mode chosen.
C1(1)
C2(1)
XTAL
OSC2
OSC1
RF(3)
Sleep
To
Logic
PIC18FXXJ6X
RS(2)
Internal
Note 1:
Higher capacitance increases the stabil-
ity of the oscillator but also increases the
start-up time.
2:
Since each crystal has its own character-
istics, the user should consult the crystal
manufacturer for appropriate values of
external components.
3:
Rs may be required to avoid overdriving
crystals with low drive level specifications.
4:
Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
OSC1/CLKI
OSC2/CLKO
FOSC/4
Clock from
Ext. System
PIC18FXXJ6X
OSC1
OSC2
Open
Clock from
Ext. System
PIC18FXXJ6X
(HS Mode)