PIC16F628 datasheet(96/170 Pages) MICROCHIP

96 / 170 page

PIC16F62X

DS40300C-page 94

Preliminary

 2003 Microchip Technology Inc.

FIGURE 14-2:

EXTERNAL PARALLEL

RESONANT CRYSTAL

OSCILLATOR CIRCUIT

Figure 14-3 shows a series resonant oscillator circuit.

This circuit is also designed to use the fundamental

frequency of the crystal. The inverter performs a 180

phase shift in a series resonant oscillator circuit. The

330 k

Ω resistors provide the negative feedback to bias

the inverters in their linear region.

FIGURE 14-3:

EXTERNAL SERIES

RESONANT CRYSTAL

OSCILLATOR CIRCUIT

14.2.4

EXTERNAL CLOCK IN

For applications, where a clock is already available

elsewhere, users may directly drive the PIC16F62X

provided that this external clock source meets the

AC/DC timing requirements listed in Section 17.4.

Figure 14-4 shows how an external clock circuit should

be configured.

FIGURE 14-4:

EXTERNAL CLOCK INPUT

OPERATION (EC, HS, XT

OR LP OSC

CONFIGURATION)

14.2.5

ER OSCILLATOR

For timing insensitive applications, the ER (External

Resistor) Clock mode offers additional cost savings.

Only one external component, a resistor to V

SS, is

needed to set the operating frequency of the internal

oscillator. The resistor draws a DC bias current which

controls the oscillation frequency. In addition to the

resistance value, the oscillator frequency will vary from

unit to unit, and as a function of supply voltage and

temperature. Since the controlling parameter is a DC

current and not a capacitance, the particular package

type and lead frame will not have a significant effect on

the resultant frequency.

Figure 14-5 shows how the controlling resistor is

connected to the PIC16F62X. For R

EXT values below

10k, the oscillator operation becomes sensitive to

temperature. For very high R

EXT values (e.g., 1M), the

oscillator becomes sensitive to leakage and may stop

completely. Thus, we recommend keeping R

EXT

between 10k and 1M.

FIGURE 14-5:

EXTERNAL RESISTOR

Table 14-3

shows

the

relationship

between

the

resistance value and the operating frequency.

TABLE 14-3:

RESISTANCE AND

FREQUENCY RELATIONSHIP

The ER Oscillator mode has two options that control

the unused OSC2 pin. The first allows it to be used as

a general purpose I/O port. The other configures the

pin as an output providing the F

OSC signal (internal

clock divided by 4) for test or external synchronization

purposes.

+5V

10K

4.7K

10K

74AS04

XTAL

10K

74AS04

PIC16F62X

CLKIN

TO OTHER

DEVICES

330 K

Ω

74AS04

PIC16F62X

CLKIN

TO OTHER

DEVICES

XTAL

330 K

Ω

74AS04

0.1 PF

Clock From

ext. system

PIC16F62X

OSC1/RA7

OSC2/RA6

RA6

Resistance

Frequency

010.4 MHz

10 MHz

10K

7.4 MHz

20K

5.3 MHz

47K

3 MHz

100K

1.6 MHz

220K

800 kHz

470K

300 kHz

200 kHz

RA7/OSC1/CLKIN

RA6/OSC2/CLKOUT

PIC16F628 Datasheet(PDF) 96 Page - Microchip Technology

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