HC705JB2GRSSLASHH datasheet(17/128 Pages) NXP

17 / 128 page

August 28, 1998

GENERAL RELEASE SPECIFICATION

GENERAL DESCRIPTION

REV 1.1

1-5

A crystal as shown in Figure 1-3(a)

A ceramic resonator as shown in Figure 1-3(a)

An external clock signal as shown in Figure 1-3(b)

The frequency, fOSC, of the oscillator or external clock source is divided by two to

produce the internal operating frequency, fOP. If the internal operating frequency is

3MHZ, then the external oscillator frequency will be 6MHz. For LS USB 1.5MHz

frequency clock can be derived from a divided by 4 circuit. The type of oscillator is

selected by a mask option.

1.4.2.1

Crystal Oscillator

The circuit in Figure 1-3(a) shows a typical oscillator circuit for an AT-cut, parallel

resonant crystal. The crystal manufacturer’s recommendations should be

followed, as the crystal parameters determine the external component values

required to provide maximum stability and reliable start-up. The load capacitance

values used in the oscillator circuit design should include all stray capacitances.

The crystal and components should be mounted as close as possible to the pins

for start-up stabilization and to minimize output distortion. An internal start-up

resistor of typically 2M

Ω is provided between OSC1 and OSC2 for the crystal type

oscillator.

Figure 1-3. Oscillator Connections

1.4.2.2

Ceramic Resonator Oscillator

In cost-sensitive applications, a ceramic resonator can be used in place of the

crystal. The circuit in Figure 1-3(a) can be used for a ceramic resonator. The

resonator manufacturer’s recommendations should be followed, as the resonator

parameters determine the external component values required for maximum

stability and reliable starting. The load capacitance values used in the oscillator

circuit design should include all stray capacitances. The ceramic resonator and

MCU

37 pF

Ω

unconnected

External Clock

OSC1

OSC2

MCU

(a) Crystal or Ceramic Resonator

Connections

(b) External Clock

Source Connection

OSC1

OSC2

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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