HC705J2 datasheet(13/78 Pages) MOTOROLA

13 / 78 page

MOTOROLA

DESCRIPTIONS

MC68HC705J2

2-2

2.1 VDD and VSS

VDD and VSS are the power supply and ground pins. The MCU operates from a

single 5-V power supply.

Very fast signal transitions occur on the MCU pins. The short rise and fall times

place very high short-duration current demands on the power supply.

prevent noise problems, take special care to provide good power supply

bypassing at the MCU.

Use bypass capacitors with good high-frequency

characteristics, and position them as close to the MCU as possible. Bypassing

requirements vary, depending on how heavily loaded the MCU pins are.

2.2 OSC1 and OSC2

The OSC1 and OSC2 pins are the control connections for the on-chip oscillator.

Connect any of the following to the OSC1 and OSC2 pins:

• A crystal (Refer to Figure 2-2.)

• A ceramic resonator (Refer to Figure 2-2.)

• An external clock signal (Refer to Figure 2-3.)

The MCU divides the frequency, fosc, of the oscillator or external clock source

by two to produce the internal operating frequency, fop.

2.2.1 Crystal

The circuit in Figure 2-2 shows a typical crystal oscillator circuit for a parallel

resonant crystal. Follow the crystal supplier's recommendations, 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 layout capacitances. Mount

the crystal and components as close as possible to the pins for start-up

stabilization and to minimize output distortion.

2.2.2 Ceramic Resonator

In cost-sensitive applications, use a ceramic resonator in place of the crystal.

Use the circuit in Figure 2-2 for a ceramic resonator, and follow the resonator

manufacturer's recommendations, 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 layout capacitances.

HC705J2 Datasheet(PDF) 13 Page - Motorola, Inc