ISO/IEC INTERNATIONAL STANDARD 9549 First edition 1990-10-15 Information technology -- Galvanic isolation of balanced interchange circuits Systemes de traitement de I'information --- solation galvanique des circuits d'échange equilibres Referencenumber ISO/IEC9549:1990(E) Copyright Intermational Organization for Standardization 'rovided by IHS cense with I3 rmitted without license from IHS Not for Resale ISO/IEC9549:1990(E) Foreword iso (the International Organization for Standardization)and IEC (the InternationaiEiectrotechnicaiCommission)formthespecializedsystem for worldwide standardization. National bodies that are members of IsO orIECparticipate inthedevelopment of International Standardsthrough withparticularfieldsoftechnicalactivity.IsOandlECtechnicalcom- mittees colliaborate in fields of mutual interest. Other international or- ganizations, governmental and non-governmentai, in liaison with Iso and iEC, aliso take part in the work. In the field of information technology, isO and IEC have established a joint technical committee, ISO/IEC JTC 1. Draft Internationai Standards adopted by the joint technical committee are circulated to national bod- ies for voting. Publication as an international Standard requires ap- proval by at least 75 % of the national bodies casting a vote International Standard ISO/IEC 9549 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology. Annex A of this international Standard is for information only C ISO/EC 1990 All rights reserved. No part of this pubiication may be reproduced or utilized in any form or by any means, electronic or mechanical, inctuding photocopying and microtitm, without permission inwriting fromthepublisher. ISO/IEC Copyright Office · Case Postale 56 · CH-1211 Geneve 20 · Switzerland Printed inSwitzerland ii r Standardizatio ng permitted without license from IHS Not for Resale ISO/1EC9549:1990(E) Introduction This Internationai Standard specifies a method of galivanically isolating signal exchanges on balanced interchange code (e.g. NRZ), Galvanic isolation of interchange circuits is required whenever the intercommunicating devices are connected to different mains supplies. In this case, the ground potential difference between the earthing systems frequently is damage to the receiver may be the result. minimized. This situation may exist with iong interchange circuits and operation at higher data signalling rates. The specifications of this International Standard are compatible with both IsO 8482 (multipoint connection) and CCITT Recommendation V.11 (point-to-point connection) because of application fiexibility and the fact that there is not much difference in the parameters for the component design. Bidirectional data transmission is provided and requires the implementation of an isolated generator and an isolated receiver. Their unbalanced interfaces are not specified in order tc provide flexibility for implementations and device manutacturers. i Copyright IntemationalOrganizationfor Standardizatior