PIC18F2331_10 Datasheet, PDF (31/392 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High-Performance PWM and A/D

PIC18F2331/2431/4331/4431
3.4 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 3-4 shows the pin connections for the EC
Oscillator mode.
FIGURE 3-4:
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 3-5 shows the pin connections
for the ECIO Oscillator mode.
FIGURE 3-5:
EXTERNAL CLOCK INPUT
OPERATION
(ECIO CONFIGURATION)
Clock from
Ext. System
RA6
OSC1/CLKI
PIC18FXXXX
I/O (OSC2)
3.5 RC Oscillator
For timing-insensitive applications, the “RC” and “RCIO”
device options offer additional cost savings. The actual
oscillator frequency is a function of several factors:
• Supply voltage
• Values of the external resistor (REXT) and capacitor
(CEXT)
• Operating temperature
Given the same device, operating voltage and tempera-
ture, and component values, there will also be unit-to-unit
frequency variations. These are due to factors, such as:
• Normal manufacturing variation
• Difference in lead frame capacitance between
package types (especially for low CEXT values)
• Variations within the tolerance of limits of REXT
and CEXT
In the RC Oscillator mode (Figure 3-6), 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 3-6:
VDD
RC OSCILLATOR MODE
REXT
OSC1
Internal
Clock
CEXT
VSS
PIC18FXXXX
OSC2/CLKO
FOSC/4
Recommended values: 3 k  REXT  100 k
CEXT > 20 pF
The RCIO Oscillator mode (Figure 3-7) 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 3-7:
VDD
RCIO OSCILLATOR MODE
REXT
OSC1
Internal
Clock
CEXT
VSS
RA6
PIC18FXXXX
I/O (OSC2)
Recommended values: 3 k  REXT  100 k
CEXT > 20 pF
 2010 Microchip Technology Inc.
DS39616D-page 31