PIC16F87 datasheet(36/230 Pages) MICROCHIP

36 / 230 page

PIC16F87/88

DS30487D-page 36

 2002-2013 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



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

 to 10 M.

C1(1)

C2(1)

RES

OSC2

RS(2)

OSC1

RF(3)

Sleep

To Internal

Logic

PIC16F87/88

OSC1/CLKI

I/O (OSC2)

RA6

Clock from

Ext. System

PIC16F87/88

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