PIC18LF8720 Microchip Technology, PIC18LF8720 Datasheet - Page 24

• Manufacturer Part Number: PIC18LF8720
• Description: (PIC18LF6620/6520/8520/6620/8620/6720/8720) 64/80-Pin High-Performance / 64-Kbyte Enhanced Flash Microcontrollers
• Manufacturer: Microchip Technology

PIC18F6520/8520/6620/8620/6720/8720
TABLE 2-2:
An external clock source may also be connected to the
OSC1 pin in the HS, XT and LP modes, as shown in
Figure 2-2.
DS39609B-page 22
Capacitor values are for design guidance only.
These capacitors were tested with the above crystal
frequencies 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
V
See the notes following this table for additional
information.
DD
Note 1: Higher capacitance increases the stability
Mode
HS
LP
XT
and temperature range for the application.
2: When operating below 3V V
3: Since each resonator/crystal has its
4: R
5: Always verify oscillator performance over
of the oscillator, but also increases the
start-up time.
using certain ceramic resonators at any
voltage, it may be necessary to use the
HS mode or switch to a crystal oscillator.
own characteristics, the user should
consult the resonator/crystal manufac-
turer for appropriate values of external
components,
performance.
crystals with low drive level specification.
the V
expected for the application.
S
200 kHz
20 MHz
32 kHz
1 MHz
4 MHz
4 MHz
8 MHz
may be required to avoid overdriving
Freq
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
DD
Ranges Tested:
and temperature range that is
15-22 pF
15-22 pF
15-22 pF
or
C1
verify
DD
15-22 pF
15-22 pF
15-22 pF
, or when
oscillator
C2
FIGURE 2-2:
2.3
For timing insensitive applications, the “RC” and
“RCIO” device options offer additional cost savings.
The RC oscillator frequency is a function of the supply
voltage, the resistor (R
ues and the operating temperature. In addition to this,
the oscillator frequency will vary from unit to unit, due
to normal process parameter variation. Furthermore,
the difference in lead frame capacitance between pack-
age types will also affect the oscillation frequency,
especially for low C
take into account variation due to tolerance of external
R and C components used. Figure 2-3 shows how the
R/C combination is connected.
In the RC 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 2-3:
The RCIO Oscillator mode functions like the RC mode,
except that the OSC2 pin becomes an additional
general purpose I/O pin. The I/O pin becomes bit 6 of
PORTA (RA6).
C
V
Recommended values:
R
Clock from
Ext. System
EXT
SS
EXT
V
DD
RC Oscillator
Open
F
OSC
EXT
/4
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC CONFIGURATION)
RC OSCILLATOR MODE
OSC1
OSC2/CLKO
EXT
values. The user also needs to
 2004 Microchip Technology Inc.
3 k
C
EXT
) and capacitor (C
OSC1
OSC2
> 20 pF
R
EXT
PIC18FXX20
PIC18FXX20
100 k
Internal
Clock
EXT
) val-