CD74HC191E datasheet, PDF - EEWORLD Datasheet

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CD74HC191E: DescriptionCounter,; Categorylogic logic; File Size151KB，21 Pages; ManufacturerGeneral Electric Solid State

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Live Insertion

SDYA012

October 1996

IMPORTANT NOTICE

Texas Instruments (TI) reserves the right to make changes to its products or to discontinue any

semiconductor product or service without notice, and advises its customers to obtain the latest

version of relevant information to verify, before placing orders, that the information being relied

on is current.

TI warrants performance of its semiconductor products and related software to the specifications

applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality

control techniques are utilized to the extent TI deems necessary to support this warranty.

Specific testing of all parameters of each device is not necessarily performed, except those

mandated by government requirements.

Certain applications using semiconductor products may involve potential risks of death,

personal injury, or severe property or environmental damage (“Critical Applications”).

TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED, OR

WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT APPLICATIONS, DEVICES

OR SYSTEMS OR OTHER CRITICAL APPLICATIONS.

Inclusion of TI products in such applications is understood to be fully at the risk of the customer.

Use of TI products in such applications requires the written approval of an appropriate TI officer.

Questions concerning potential risk applications should be directed to TI through a local SC

sales office.

In order to minimize risks associated with the customer’s applications, adequate design and

operating safeguards should be provided by the customer to minimize inherent or procedural

hazards.

TI assumes no liability for applications assistance, customer product design, software

performance, or infringement of patents or services described herein. Nor does TI warrant or

represent that any license, either express or implied, is granted under any patent right, copyright,

mask work right, or other intellectual property right of TI covering or relating to any combination,

machine, or process in which such semiconductor products or services might be or are used.

1996, Texas Instruments Incorporated

Contents

Title

Page

Abstract

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 Introduction

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Internal Construction of Integrated Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Operating Conditions When Changing Modules With the Supply Voltage On

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1 GND and the signal line (SL) make contact first; the output of circuit N1 is low

. . . . . . . . . . . . . . . . . . . . . . . . . .

3.2 V

and the signal line (SL) make contact first; the output of circuit N1 is low

. . . . . . . . . . . . . . . . . . . . . . . . . . .

3.3 GND and the signal line (SL) make contact first; the output of circuit N1 is high

. . . . . . . . . . . . . . . . . . . . . . . . .

3.4 V

and the signal line (SL) make contact first; the output of circuit N1 is high

. . . . . . . . . . . . . . . . . . . . . . . . . .

3.5 V

and GND make contact first . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Simple Circuit Modifications

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Avoidance of Bus Conflicts

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 Avoidance of Disturbances on the System Bus

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 Special Bus-Interface Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 Avoidance of Disturbances to the Supply Voltage

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 Summary

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acknowledgment

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

List of Illustrations

Figure

Title

Page

Diodes in the Inputs and Outputs of Integrated Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voltage-Monitoring Circuit in BiCMOS ICs

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Simplified Circuit to Show Current Paths When Connecting a Module to a System

. . . . . . . . . . . . . . . . . . . . . . . . .

Improved Circuit Using Bipolar or BiCMOS Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Curve for Calculating the Short-Circuit Currents That Occur With Bus Conflicts

. . . . . . . . . . . . . . . . . . . . . . . . . . .

Monitoring Bus-Interface Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Connecting a Capacitor to a Line

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voltage Peaks When Making Contacts to Signal Lines (Without Voltage Bias)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Connection of a Capacitor to a Line (With Voltage Bias)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Voltage Peaks When Making Contacts to Signal Lines (With Voltage Bias)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Generation of the Voltage Bias and Control of the Interface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Generation of the Voltage Bias and Control in the SN74ABTE16245

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Bus-Interface Control in ETL Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Bus-Interface Control With BTL Circuits

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Widebus is a trademark of Texas Instruments Incorporated.

iii

List of Illustrations (Continued)

Equivalent Circuit of the Current Supply to a Module

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Transient Behavior of the Supply Voltage at Switch On, With Various Degrees of Damping

. . . . . . . . . . . . . . . . .

Switch-On Delay Circuit Using a MOS Transistor

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Decentralized Power Supply With Limiting of Switch-On Current

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Abstract

In many current applications, there is a requirement to exchange modules in electronic systems while the supply voltage

remains on. This procedure is commonly known as live insertion. To understand this requirement, consider the case of an

electronic telephone exchange in which replacing modules for maintenance or repair must be possible at any time without

interrupting the operation of the system. To avoid damage to components, and any interruption of operation when changing

modules in this way, additional circuitry modifications are necessary.

This report describes the phenomena that occur during live insertion, then presents circuit proposals to solve the potential

problems that might otherwise arise.

1 Introduction

For many years, diverse functions and processes have been monitored and controlled successfully by electronic systems. The

advantages of electronic controls in such cases (compared with manual or mechanical controls) are lower operating costs and

the improved reliability that electronics now provide. However, faults also can arise in such electronic systems, which then

require repair. By using modular construction for the equipment, it is possible to quickly exchange a defective module and clear

the fault.

With most equipment, it is necessary to switch off the supply voltage during the exchange of the modules to avoid incorrect

operation or destruction of components. In many cases–an obvious example is the computer in an office–the exchange of

modules while the equipment is turned off is permissible.

In many electronic systems, switching off the equipment to exchange a defective module is unacceptable. Examples include

an electronic telephone exchange, the switching control center of an electric utility, or the computer that processes data in the

air-traffic control center of an airport. In all of these cases, when a fault is found in a module, exchanging this module in a

running system without disturbing or otherwise compromising the rest of the system functions must be possible.

The engineer planning and developing electronic systems for such applications must consider the operating states that can arise

and meet these requirements by choosing appropriate components and circuitry layout.

A distinction must be made at this point between two different cases. In the first, it is necessary only to ensure that a module

or a part of the installation can be exchanged during operation without switching off the system and without damaging it. In

such cases, it can be acceptable (for reasons described later) that the operation of the equipment is disturbed. An example is

the installation or exchange of a printer for an operating office computer. The primary requirement is the simple and safe

operation of the entire system; in this case, the requirements can be fulfilled by choosing appropriate components for

the interfaces.

In the second case, the additional requirement must be met that, during exchange of the modules, the components involved

should neither be damaged, nor should the operation be disturbed. To ensure this, beside choosing the appropriate components,

the development engineer also must incorporate additional circuit modifications to allow continuous and reliable operation

of the system.

This applications report provides the development engineer with suggestions for fulfilling these requirements. The report

begins with the choice of the most appropriate components for the application, and continues with a description of circuit

modifications that are necessary under the operating conditions described.

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