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2002 Microchip Technology Inc.
Preliminary
DS30485A-page 19
PIC18FXX39
2.0
OSCILLATOR
CONFIGURATIONS
2.1
Oscillator Types
The PIC18FXX39 can be operated in four different
Oscillator modes at a frequency of 20 MHz. The user
can program three configuration bits (FOSC2, FOSC1,
and FOSC0) to select one of these four modes:
1.
HS
High Speed Crystal/Resonator
2.
HS + PLL
High Speed Crystal/Resonator
with PLL enabled using 5 MHz
crystal
3.
EC
External Clock
4.
ECIO
External Clock with I/O pin
enabled
2.2
Crystal Oscillator/Ceramic
Resonators
In HS or HS+PLL 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 PIC18FXX39 oscillator design requires the use of
a parallel cut crystal.
FIGURE 2-1:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS CONFIGURATION)
An external clock source may also be connected to the
OSC1 pin in the HS mode, as shown in Figure 2-2.
FIGURE 2-2:
EXTERNAL CLOCK INPUT
OPERATION (HS OSC
CONFIGURATION)
Note:
The operation of the Motor Control kernel
and its APIs (Section 14.0) is based on an
assumed clock frequency of 20 MHz.
Changing the oscillator frequency will
change the timing used in the Motor Con-
trol kernel accordingly. To achieve the best
results in motor control applications, a
clock frequency of 20 MHz is highly
recommended.
Note:
Use of a series cut crystal may give a fre-
quency out of the crystal manufacturers
specifications.
Note 1: Higher capacitance 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 appro-
priate values of external components, or
verify oscillator performance.
Note 1: See Table 2-1 for recommended 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.
C1(1)
C2(1)
XTAL
OSC2
OSC1
RF(3)
SLEEP
To
Logic
PIC18FXX39
RS(2)
Internal
OSC1
OSC2
Open
Clock from
Ext. System
PIC18FXX39
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