PIC18F2331 Datasheet, PDF (25/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
2.4 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 2-4 shows the pin connections for the EC
Oscillator mode.
FIGURE 2-4:
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 2-5 shows the pin connections
for the ECIO Oscillator mode.
FIGURE 2-5:
EXTERNAL CLOCK INPUT
OPERATION
(ECIO CONFIGURATION)
Clock from
Ext. System
RA6
OSC1/CLKI
PIC18FXXXX
I/O (OSC2)
2.5 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 manufacturing variation. Furthermore,
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 2-6 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 2-6:
VDD
RC OSCILLATOR MODE
REXT
OSC1
Internal
Clock
CEXT
VSS
OSC2/CLKO
FOSC/4
PIC18FXXXX
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20 pF
The RCIO Oscillator mode (Figure 2-7) 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).
FIGURE 2-7:
VDD
REXT
CEXT
VSS
RA6
RCIO OSCILLATOR MODE
OSC1
Internal
Clock
I/O (OSC2)
PIC18FXXXX
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
CEXT > 20 pF
 2003 Microchip Technology Inc.
Preliminary
DS39616B-page 23