PIC18F258 Datasheet, PDF (20/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN

PIC18FXX8
TABLE 2-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq
Cap. Range Cap. Range
C1
C2
LP
32.0 kHz
33 pF
33 pF
200 kHz
15 pF
15 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
TBD
TBD
HS+PLL 4.0 MHz
15 pF
15 pF
8.0 MHz 15-33 pF 15-33 pF
10.0 MHz
TBD
TBD
These values are for design guidance only.
See notes on this page.
Crystals Used
32.0 kHz
200 kHz
1.0 MHz
4.0 MHz
8.0 MHz
20.0 MHz
Epson C-001R32.768K-A
STD XTL 200.000KHz
ECS ECS-10-13-1
ECS ECS-40-20-1
EPSON CA-301 8.000M-C
EPSON CA-301 20.000M-
C
± 20 PPM
± 20 PPM
± 50 PPM
± 50 PPM
± 30 PPM
± 30 PPM
Note 1: Recommended values of C1 and C2 are
identical to the ranges tested (Table 2-1).
2: Higher capacitance increases the stability
of the oscillator, but also increases the
start-up time.
3: Since each resonator/crystal has its own
characteristics, the user should consult the
resonator/crystal manufacturer for
appropriate values of external components.
4: Rs may be required in HS mode, as well as
XT mode, to avoid overdriving crystals with
low drive level specification.
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) val-
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 package
types will also affect the oscillation frequency, espe-
cially for low CEXT values. The user also needs to take
into account variation due to tolerance of external R
and C components used. Figure 2-2 shows how the RC
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 2-2:
RC OSCILLATOR MODE
VDD
REXT
CEXT
VSS
OSC1
PIC18FXX8
Internal
Clock
OSC2/CLKO
FOSC/4
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
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.
DS41159B-page 18
Preliminary
 2002 Microchip Technology Inc.