IEC_TR_61131-8-2003.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)LICENSED TO MECON Limited.-RANCHI/BANGALOREFOR INTERNAL USE AT THIS LOCATION ONLY,SUPPLIED BY BOOK SUPPLY BUREAU.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committees and date of publication.On-line information is also available on recently issued publications,withdrawn and replaced publications,as well as corrigenda.IEC Just Published This summary of recently issued publications(www.iec.ch/online_news/justpub)is also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 LICENSED TO MECON Limited.-RANCHI/BANGALOREFOR INTERNAL USE AT THIS LOCATION ONLY,SUPPLIED BY BOOK SUPPLY BUREAU.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 LICENSED TO MECON Limited.-RANCHI/BANGALOREFOR INTERNAL USE AT THIS LOCATION ONLY,SUPPLIED BY BOOK SUPPLY BUREAU.2 TR 61131-8 IEC:2003(E)CONTENTS FOREWORD.6 INTRODUCTION.8 1 General.9 1.1 Scope.9 1.2 Normative references.9 1.3 Abbreviated terms.9 1.4 Overview.10 2 Introduction to IEC 61131-3.10 2.1 General considerations.10 2.2 Overcoming historical limitations.12 2.3 Basic features in IEC 61131-3.13 2.4 New features in the second edition of IEC 61131-3.14 2.5 Software engineering considerations.14 2.5.1 Application of software engineering principles.14 2.5.2 Portability.17 3 Application guidelines.17 3.1 Use of data types.17 3.1.1 Type versus variable initialization.18 3.1.2 Use of enumerated and subrange types.18 3.1.3 Use of BCD data.19 3.1.4 Use of REAL data types.21 3.1.5 Use of character string data types.21 3.1.6 Use of time data types.22 3.1.7 Declaration and use of multi-element variables.22 3.1.8 Use of bit-string functions.23 3.1.9 Strongly typed assignment.24 3.2 Data passing.25 3.2.1 Global and external variables.25 3.2.2 In-out(VAR_IN_OUT)variables.26 3.2.3 Formal and non-formal invocations and argument lists.28 3.3 Use of function blocks.30 3.3.1 Function block types and instances.30 3.3.2 Scope of data within function blocks.31 3.3.3 Function block access and invocation.32 3.4 Differences between function block instances and functions.33 3.5 Use of indirectly referenced function block instances.33 3.5.1 Establishing an indirect function block instance reference.34 3.5.2 Access to indirectly referenced function block instances.35 3.5.3 Invocation of indirectly referenced function block instances.35 3.5.4 Recursion of indirectly referenced function block instances.38 3.5.5 Execution control of indirectly referenced function block instances.38 3.5.6 Use of indirectly referenced function block