PIC18F6525_13 Datasheet, PDF (22/400 Pages) Microchip Technology – 64/80-Pin High-Performance, 64-Kbyte Enhanced Flash Microcontrollers with A/D

PIC18F6525/6621/8525/8621
TABLE 2-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Ranges Tested:
Mode
Freq
C1
C2
LP
32.0 kHz
33 pF
33 pF
XT
200 kHz 47-68 pF 47-68 pF
1.0 MHz
15 pF
15 pF
4.0 MHz
15 pF
15 pF
HS
4.0 MHz
15 pF
15 pF
8.0 MHz 15-33 pF 15-33 pF
20.0 MHz 15-33 pF 15-33 pF
25.0 MHz 15-33 pF 15-33 pF
These values are for design guidance only.
See notes following this table.
Crystals Used
32 kHz
200 kHz
1 MHz
4 MHz
8 MHz
20 MHz
Note 1: Higher capacitance increases the stability
of the oscillator but also increases the
start-up time.
2: RS (see Figure 2-1) may be required in
HS mode, as well as XT mode, to avoid
overdriving crystals with low drive level
specification.
3: 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.
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.
FIGURE 2-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSCILLATOR
CONFIGURATION)
Clock from
Ext. System
Open
OSC1
PIC18F6X2X/8X2X
OSC2
2.3 RC Oscillator
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 (REXT) and capacitor (CEXT)
values and the operating temperature. In addition to
this, the oscillator frequency will vary from unit to unit
due to normal process parameter variation. Further-
more, the difference in lead frame capacitance
between package types will also affect the oscillation
frequency, especially for low CEXT values. The user
also needs to 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:
VDD
RC OSCILLATOR MODE
REXT
OSC1
Internal
Clock
CEXT
VSS
PIC18F6X2X/8X2X
OSC2/CLKO
FOSC/4
Recommended values: 3 k  REXT  100 k
CEXT > 20 pF
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).
DS39612C-page 22
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