PIC18FXX8 Datasheet, PDF (20/402 Pages) Microchip Technology – 28/40-Pin High-Performance, Enhanced Flash Microcontrollers with CAN Module

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 15-33 pF 15-33 pF
These values are for design guidance only.
See notes on this page.
Crystals Used
32.0 kHz Epson C-001R32.768K-A
200 kHz STD XTL 200.000KHz
1.0 MHz
ECS ECS-10-13-1
4.0 MHz
ECS ECS-40-20-1
8.0 MHz EPSON CA-301 8.000M-C
20.0 MHz 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) values 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 differ-
ence 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 2-2 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.
Note:
If the oscillator frequency divided by 4
signal is not required in the application, it
is recommended to use RCIO mode to
save current.
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. The I/O pin becomes bit 6 of
PORTA (RA6).
DS41159D-page 18
 2004 Microchip Technology Inc.