1、 IEC TR 61131-8 Edition 3.0 2017-11 TECHNICAL REPORT Industrial-process measurement and control Programmable controllers Part 8:Guidelines for the application and implementation of programming languages IEC TR 61131-8:2017-11en)colourinside THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2017 IEC,
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12、EC TR 61131-8:2017 IEC 2017 CONTENTS FOREWORD.6 INTRODUCTION.8 1 Scope.9 2 Normative references.9 3 Terms and definitions.9 4 Abbreviated terms.9 5 Overview.10 6 Introduction to IEC 61131-3.10 6.1 General considerations.10 6.2 Overcoming historical limitations.13 6.3 Basic features in IEC 61131-3.13
13、 6.4 Language items overview.14 6.5 Changes from IEC 61131-3:2003(edition 2)to IEC 61131-3:2013(edition 3).16 6.6 Software engineering considerations.17 6.6.1 Application of software engineering principles.17 6.6.2 Portability.19 7 Application guidelines.20 7.1 Use of data types.20 7.1.1 Type select
14、ion.20 7.1.2 Type versus variable initialization.20 7.1.3 Use of enumerated and subrange types.21 7.1.4 Use of BCD data.22 7.1.5 Use of REAL data types.22 7.1.6 Use of character string data types.23 7.1.7 Use of character data types.24 7.1.8 Use of time data types.24 7.1.9 Declaration and use of mul
15、ti-element variables.26 7.1.10 Use of bit-string variables.26 7.1.11 Use of partial accessing of bitstring variables.27 7.1.12 Type assignment.27 7.2 Data passing over POU.27 7.2.1 General.27 7.2.2 External variables.29 7.2.3 In-out(VAR_IN_OUT)variables.29 7.2.4 Formal and non-formal invocations and
16、 argument lists.32 7.2.5 Assignment of input,output,and in-out variables of programs.34 7.3 Use of function blocks.35 7.3.1 Function block types and instances.35 7.3.2 Scope of data within function blocks.35 7.3.3 Function block access and invocation.36 7.4 Differences between function block instances and functions.37 7.5 Use of indirectly referenced function block instances.37 7.5.1 General.37 7.5.2 Establishing an indirect function block instance reference.38 7.5.3 Access to indirectly referen
