PIC16F818-ESLASHML datasheet(36/176 Pages) MICROCHIP

36 / 176 page

PIC16F818/819

DS39598E-page 34

 2004 Microchip Technology Inc.

FIGURE 4-2:

CERAMIC RESONATOR

OPERATION (HS OR XT

OSC CONFIGURATION)

TABLE 4-2:

CERAMIC RESONATORS (FOR

DESIGN GUIDANCE ONLY)

4.3

External Clock Input

The ECIO Oscillator mode requires 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 ECIO Oscillator mode, the OSC2 pin becomes

an additional general purpose I/O pin. The I/O pin

becomes bit 6 of PORTA (RA6). Figure 4-3 shows the

pin connections for the ECIO Oscillator mode.

FIGURE 4-3:

EXTERNAL CLOCK INPUT

OPERATION

(ECIO CONFIGURATION)

Typical Capacitor Values Used:

Mode

Freq

OSC1

OSC2

455 kHz

2.0 MHz

4.0 MHz

56 pF

47 pF

33 pF

56 pF

47 pF

33 pF

8.0 MHz

16.0 MHz

27 pF

22 pF

27 pF

22 pF

Capacitor values are for design guidance only.

These capacitors were tested with the resonators

listed below for basic start-up and operation. These

values were not optimized.

Different capacitor values may be required to produce

acceptable oscillator operation. The user should test

the performance of the oscillator over the expected

VDD and temperature range for the application.

See the notes following this table for additional

information.

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. If HS is selected, it is

possible that the gain of the oscillator will

overdrive the resonator. Therefore, a

series resistor should be placed between

the OSC2 pin and the resonator. As a

good starting point, the recommended

value of RS is 330

Ω.

Note 1:

See Table 4-2 for typical values of C1 and C2.

2: A series resistor (RS) may be required.

3: RF varies with the resonator chosen (typically

between 2 M

Ω to 10 MΩ).

C1(1)

C2(1)

RES

OSC2

RS(2)

OSC1

RF(3)

Sleep

To Internal

Logic

PIC16F818/819

OSC1/CLKI

I/O (OSC2)

RA6

Clock from

Ext. System

PIC16F818/819

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