PIC16F84AT-20SLASHSSROM datasheet(24/88 Pages) MICROCHIP

24 / 88 page

PIC16F84A

DS35007B-page 22

6.2

Oscillator Configurations

6.2.1

OSCILLATOR TYPES

The PIC16F84A can be operated in four different

oscillator

modes.

The

user

can

program

two

configuration bits (FOSC1 and FOSC0) to select one of

these four modes:

• LP

Low Power Crystal

• XT

Crystal/Resonator

• HS

High Speed Crystal/Resonator

• RC

Resistor/Capacitor

6.2.2

CRYSTAL OSCILLATOR/CERAMIC

RESONATORS

In XT, LP, or HS modes, a crystal or ceramic resonator

is connected to the OSC1/CLKIN and OSC2/CLKOUT

pins to establish oscillation (Figure 6-1).

FIGURE 6-1:

CRYSTAL/CERAMIC

RESONATOR OPERATION

(HS, XT OR LP OSC

CONFIGURATION)

The PIC16F84A oscillator design requires the use of a

parallel cut crystal. Use of a series cut crystal may give

frequency

out

the

crystal

manufacturers

specifications. When in XT, LP, or HS modes, the

device can have an external clock source to drive the

OSC1/CLKIN pin (Figure 6-2).

FIGURE 6-2:

EXTERNAL CLOCK INPUT

OPERATION (HS, XT OR

LP OSC

CONFIGURATION)

TABLE 6-1:

CAPACITOR SELECTION FOR

CERAMIC RESONATORS

Note 1: See Table 6-1 for recommended values

of C1 and C2.

2: A series resistor (RS) may be required

for AT strip cut crystals.

C1(1)

C2(1)

XTAL

OSC2

OSC1

RF(3)

SLEEP

Logic

PIC16FXX

RS(2)

Internal

Ranges Tested:

Mode

Freq

OSC1/C1

OSC2/C2

455 kHz

2.0 MHz

4.0 MHz

47 - 100 pF

15 - 33 pF

47 - 100 pF

15 - 33 pF

8.0 MHz

10.0 MHz

15 - 33 pF

Note:

Recommended values of C1 and C2 are

identical to the ranges tested in this table.

Higher capacitance increases the stability

of the oscillator, but also increases the

start-up time. These values are for design

guidance only. Since each resonator has

its own characteristics, the user should

consult the resonator manufacturer for the

appropriate values of external compo-

nents.

Note:

When using resonators with frequencies

above 3.5 MHz, the use of HS mode rather

than XT mode, is recommended. HS mode

may be used at any VDD for which the

controller is rated.

OSC1

OSC2

Open

Clock from

Ext. System

PIC16FXX

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