68HC705JB3 datasheet(17/134 Pages) FREESCALE

17 / 134 page

November 5, 1998

GENERAL RELEASE SPECIFICATION

MC68HC05JB3

GENERAL DESCRIPTION

MOTOROLA

REV 1

1-5

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. An internal 2M

Ω resistor may be selected between

OSC1 and OSC2 by a mask option (crystal/ceramic resonator mode only).

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 fol-

lowed, 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 approximately 2M

Ω is provided between OSC1 and OSC2 for the crys-

tal type oscillator as a mask option.

Figure 1-3. Oscillator Connections

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 res-

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

parameters determine the external component values required for maximum sta-

bility and reliable starting. The load capacitance values used in the oscillator cir-

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

components should be mounted as close as possible to the pins for start-up stabi-

lization and to minimize output distortion. An internal start-up resistor of approxi-

mately 2 M

Ω is provided between OSC1 and OSC2 for the ceramic resonator type

oscillator as a mask option.

MCU

OSC1

OSC2

Ω

Unconnected

External Clock

MCU

OSC1

OSC2

(a) Crystal or Ceramic Resonator Connections

(b) External Clock Source Connection

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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