PIC18LC658-ESLASHCL datasheet(23/366 Pages) MICROCHIP

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 2000 Microchip Technology Inc.

Advanced Information

DS30475A-page 23

PIC18CXX8

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) val-

ues 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 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 2-2 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 2-2:

RC OSCILLATOR MODE

The RCIO oscillator mode functions like the RC mode,

except that the OSC2 pin becomes an additional gen-

eral purpose I/O pin. The I/O pin becomes bit 6 of

PORTA (RA6).

2.4

External Clock Input

The EC and ECIO oscillator modes require an external

clock source to be connected to the OSC1 pin. The

feedback device between OSC1 and OSC2 is turned

off in these modes to save current. There is no oscilla-

tor start-up time required after a Power-on Reset or

after a recovery 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 OSC CONFIGURATION)

The ECIO oscillator mode functions like the EC mode,

except that the OSC2 pin becomes an additional gen-

eral 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)

OSC2/CLKO/RA6

CEXT

REXT

PIC18CXX8

OSC1

FOSC/4

Internal

clock

VDD

VSS

Recommended values:

3 k

Ω ≤ REXT ≤ 100 kΩ

CEXT > 20pF

or I/O

OSC1

OSC2

FOSC/4

Clock from

ext. system

PIC18CXX8

OSC1

I/O (OSC2)

RA6

Clock from

ext. system

PIC18CXX8

PIC18LC658-E/CL Datasheet(PDF) 23 Page - Microchip Technology

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