PIC16C745SLASHP datasheet(96/158 Pages) MICROCHIP

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PIC16C745/765

DS41124A-page 96

Advanced Information

13.2

Oscillator Configurations

13.2.1

OSCILLATOR TYPES

The PIC16C745/765 can be operated in four different

oscillator modes. The user can program a configuration

bit (FOSC0) to select one of these four modes:

•EC

External Clock

•E4

External Clock with PLL

•HS

High Speed Crystal/Resonator

•H4

High Speed Crystal/Resonator with PLL

13.2.2

CRYSTAL OSCILLATOR/CERAMIC

RESONATORS

In HS mode, a crystal or ceramic resonator is con-

nected to the OSC1/CLKIN and OSC2/CLKOUT pins to

establish oscillation (Figure 13-1). The PIC16C745/

765 oscillator design requires the use of a parallel cut

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

out of the crystal manufacturers specifications. When in

HS mode, the device can have an external clock source

to drive the OSC1/CLKIN pin (Figure 13-2). In this

mode, the oscillator start-up timer is active for a period

of 1024*TOSC. See the PICmicro™ Mid-Range MCU

Reference Manual (DS33023) for details on building an

external oscillator.

FIGURE 13-1: CRYSTAL/CERAMIC

RESONATOR OPERATION

(HS OSC CONFIGURATION)

TABLE 13-1:

CERAMIC RESONATORS

TABLE 13-2:

CAPACITOR SELECTION FOR

CRYSTAL OSCILLATOR

13.2.3

H4 MODE

In H4 mode, a PLL module is switched on in-line with

the clock provided across OSC1 and OCS2. The output

of the PLL drives FINT.

XTAL

OSC2

Note1

OSC1

SLEEP

To internal

logic

PIC16C745/765

Note 1:

A series resistor may be required for AT strip cut

crystals.

Ranges Tested:

Mode

Freq

OSC1

OSC2

6.0 MHz

TBD

These values are for design guidance only. See notes at

bottom of page.

Osc Type

Crystal

Freq

Cap. Range

6.0 MHz

TBD

These values are for design guidance only. See notes at

bottom of page.

Note 1: Higher capacitance increases the stability

of the oscillator, but also increases the start-

up time.

2: Since each resonator/crystal has its own

characteristics, the user should consult the

resonator/crystal manufacturer for appropri-

ate values of external components.

3: Rs may be required in HS mode to avoid

overdriving crystals with low drive level

specification.

4: When migrating from other PICmicro

devices, oscillator performance should be

verified.

5: Users should consult the USB Specification

1.0 to ensure their resonator/crystal oscilla-

tor meets the required jitter limits for USB

operation.

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