PIC18LF4331-ESLASHML datasheet(31/392 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS39616D-page 31

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)

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)

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:

RC OSCILLATOR MODE

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:

RCIO OSCILLATOR MODE

OSC1/CLKI

OSC2/CLKO

FOSC/4

Clock from

Ext. System

PIC18FXXXX

OSC1/CLKI

I/O (OSC2)

RA6

Clock from

Ext. System

PIC18FXXXX

OSC2/CLKO

CEXT

REXT

PIC18FXXXX

OSC1

FOSC/4

Internal

Clock

VDD

VSS

Recommended values: 3 k

  REXT  100 k

CEXT > 20 pF

CEXT

REXT

PIC18FXXXX

OSC1

Internal

Clock

VDD

VSS

Recommended values: 3 k

  REXT  100 k

CEXT > 20 pF

I/O (OSC2)

RA6

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