68HC705SB7 datasheet(17/170 Pages) FREESCALE

17 / 170 page

August 27, 1998

GENERAL RELEASE SPECIFICATION

MC68HC05SB7

GENERAL DESCRIPTION

MOTOROLA

REV 2.1

1-5

The frequency, fOSC of the EPO or external clock source is divided by two to pro-

duce the internal operating frequency, fOP. or fBUS.

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.

Figure 1-3. EPO 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.

External Clock

An external clock from another CMOS-compatible device can be connected to the

OSC1 input, with the OSC2 input not connected, as shown in Figure 1-3(b). This

conﬁguration is possible regardless of whether the crystal/ceramic resonator or

internal VCO is enabled.

1.6.3 IRQ/VPP

The IRQ/VPP input pin drives the asynchronous IRQ interrupt function of the CPU.

The IRQ interrupt function has a bit to provide either only negative edge-sensitive

triggering or both negative edge-sensitive and low level-sensitive triggering. If the

MCU

OSC1

OSC2

Ω

Unconnected

External Clock

MCU

OSC1

OSC2

(a) Crystal or Ceramic Resonator Connections

(b) External Clock Source Connection

68HC705SB7 Datasheet(PDF) 17 Page - Freescale Semiconductor, Inc

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