PIC18F2585_07 Datasheet, PDF (26/482 Pages) Microchip Technology – Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2585/2680/4585/4680
TABLE 2-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq
Typical Capacitor Values
Tested:
C1
C2
LP
32 kHz
33 pF
33 pF
200 kHz
15 pF
15 pF
XT
1 MHz
33 pF
33 pF
4 MHz
27 pF
27 pF
HS
4 MHz
27 pF
27 pF
8 MHz
22 pF
22 pF
20 MHz
15 pF
15 pF
Capacitor values are for design guidance only.
These capacitors were tested with the crystals listed
below 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
VDD and temperature range for the application.
See the notes following this table for additional
information.
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: When operating below 3V VDD, or when
using certain ceramic resonators at any
voltage, it may be necessary to use the
HS mode or switch to a crystal oscillator.
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 to avoid overdriving
crystals with low drive level specification.
5: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
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 OSCILLATOR
CONFIGURATION)
Clock from
Ext. System
Open
OSC1
PIC18FXXXX
OSC2 ^{(HS Mode)}
2.3 External Clock Input
The EC and ECIO Oscillator modes require an external
clock source to be connected to the OSC1 pin. There is
no oscillator start-up time required after a Power-on
Reset or after an exit from Sleep mode.
In the EC 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 shows the pin connections for the EC
Oscillator mode.
FIGURE 2-3:
EXTERNAL CLOCK
INPUT OPERATION
(EC CONFIGURATION)
Clock from
Ext. System
FOSC/4
OSC1/CLKI
PIC18FXXXX
OSC2/CLKO
The ECIO Oscillator mode functions like the EC mode,
except that the OSC2 pin becomes an additional
general purpose I/O pin. The I/O pin becomes bit 6 of
PORTA (RA6). Figure 2-4 shows the pin connections
for the ECIO Oscillator mode.
FIGURE 2-4:
EXTERNAL CLOCK
INPUT OPERATION
(ECIO CONFIGURATION)
Clock from
Ext. System
RA6
OSC1/CLKI
PIC18FXXXX
I/O (OSC2)
DS39625C-page 24
Preliminary
© 2007 Microchip Technology Inc.