PIC16F84A datasheet(25/88 Pages) MICROCHIP

25 / 88 page

DS35007B-page 23

PIC16F84A

TABLE 6-2:

CAPACITOR SELECTION

FOR CRYSTAL OSCILLATOR

6.2.3

RC OSCILLATOR

For timing insensitive applications, the RC device

option offers additional cost savings. The RC oscillator

frequency is a function of the supply voltage, the

resistor (REXT) values, capacitor (CEXT) values, and

the operating temperature. In addition to this, the oscil-

lator frequency will vary from unit to unit due to normal

process

parameter

variation.

Furthermore,

the

difference in lead frame capacitance between package

types also affects the oscillation frequency, especially

for low CEXT values. The user needs to take into

account variation, due to tolerance of the external

R and C components. Figure 6-3 shows how an R/C

combination is connected to the PIC16F84A.

FIGURE 6-3:

RC OSCILLATOR MODE

Mode

Freq

OSC1/C1

OSC2/C2

32 kHz

200 kHz

68 - 100 pF

15 - 33 pF

68 - 100 pF

15 - 33 pF

100 kHz

2 MHz

4 MHz

100 - 150 pF

15 - 33 pF

100 - 150 pF

15 - 33 pF

4 MHz

20 MHz

15 - 33 pF

Note:

Higher capacitance increases the stability

of the oscillator, but also increases the

start-up time. These values are for design

guidance only. Rs may be required in HS

mode, as well as XT mode, to avoid over-

driving crystals with low drive level specifi-

cation. Since each crystal has its own

characteristics, the user should consult the

crystal

manufacturer

for

appropriate

values of external components.

For VDD > 4.5V, C1 = C2

≈ 30 pF is recom-

mended.

OSC2/CLKOUT

CEXT

REXT

PIC16FXX

OSC1

FOSC/4

Internal

Clock

VDD

VSS

Recommended values:

5 k

Ω ≤ REXT ≤ 100 kΩ

CEXT > 20pF

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