IEC_61131-8_Programmable_controllers.pdf

TECHNICALREPORTIEC TR 61131-8Second edition2003-09Programmable controllers Part 8:Guidelines for the application and implementationof programming languagesAutomates programmables Partie 8:Lignes directrices pour lapplication et la mise en oeuvredes langages de programmationReference numberIEC/TR 61131-8:2003(E)Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=Technip Abu Dabhi/5931917101 Not for Resale,02/12/2006 07:05:04 MSTNo reproduction or networking permitted without license from IHS-,-,-Publication numbering As from 1 January 1997 all IEC publications are issued with a designation in the 60000 series.For example,IEC 34-1 is now referred to as IEC 60034-1.Consolidated editions The IEC is now publishing consolidated versions of its publications.For example,edition numbers 1.0,1.1 and 1.2 refer,respectively,to the base publication,the base publication incorporating amendment 1 and the base publication incorporating amendments 1 and 2.Further information on IEC publications The technical content of IEC publications is kept under constant review by the IEC,thus ensuring that the content reflects current technology.Information relating to this publication,including its validity,is available in the IEC Catalogue of publications(see below)in addition to new editions,amendments and corrigenda.Information on the subjects under consideration and work in progress undertaken by the technical committee which has prepared this publication,as well as the list of publications issued,is also available from the following:IEC Web Site(www.iec.ch)Catalogue of IEC publications The on-line catalogue on the IEC web site(www.iec.ch/searchpub)enables you to search by a variety of criteria including text searches,technical committees and date of publication.On-line information is also available on recently issued publications,withdrawn and replaced publications,as well as corrigenda.IEC Just Published This summary of recently issued publications(www.iec.ch/online_news/justpub)is also available by email.Please contact the Customer Service Centre(see below)for further information.Customer Service Centre If you have any questions regarding this publication or need further assistance,please contact the Customer Service Centre:Email:custserviec.ch Tel:+41 22 919 02 11 Fax:+41 22 919 03 00 Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=Technip Abu Dabhi/5931917101 Not for Resale,02/12/2006 07:05:04 MSTNo reproduction or networking permitted without license from IHS-,-,-TECHNICALREPORTIECTR 61131-8Second edition2003-09Programmable controllers Part 8:Guidelines for the application and implementationof programming languagesAutomates programmables Partie 8:Lignes directrices pour lapplication et la mise en oeuvredes langages de programmationPRICE CODE IEC 2003 Copyright-all rights reservedNo part of this publication may be reproduced or utilized in any form or by any means,electronic ormechanical,including photocopying and microfilm,without permission in writing from the publisher.International Electrotechnical Commission,3,rue de Varemb,PO Box 131,CH-1211 Geneva 20,SwitzerlandTelephone:+41 22 919 02 11 Telefax:+41 22 919 03 00 E-mail:inmailiec.ch Web:www.iec.chXDFor price,see current catalogueCommission Electrotechnique InternationaleInternational Electrotechnical Commission Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=Technip Abu Dabhi/5931917101 Not for Resale,02/12/2006 07:05:04 MSTNo reproduction or networking permitted without license from IHS-,-,-2 TR 61131-8 IEC:2003(E)CONTENTSFOREWORD.6INTRODUCTION.81General.91.1Scope.91.2Normative references.91.3Abbreviated terms.91.4Overview.102Introduction to IEC 61131-3.102.1General considerations.102.2Overcoming historical limitations.122.3Basic features in IEC 61131-3.132.4New features in the second edition of IEC 61131-3.142.5Software engineering considerations.142.5.1Application of software engineering principles.142.5.2Portability.173Application guidelines.183.1Use of data types.183.1.1Type versus variable initialization.183.1.2Use of enumerated and subrange types.183.1.3Use of BCD data.193.1.4Use of REAL data types.213.1.5Use of character string data types.213.1.6Use of time data types.233.1.7Declaration and use of multi-element variables.233.1.8Use of bit-string functions.243.1.9Strongly typed assignment.253.2Data passing.263.2.1Global and external variables.273.2.2In-out(VAR_IN_OUT)variables.273.2.3Formal and non-formal invocations and argument lists.303.3Use of function blocks.323.3.1Function block types and instances.323.3.2Scope of data within function blocks.333.3.3Function block access and invocation.343.4Differences between function block instances and functions.353.5Use of indirectly referenced function block instances.353.5.1Establishing an indirect function block instance reference.353.5.2Access to indirectly referenced fu