MODBUS Messaging on TCP/IP Implementation Guide V1.0b
Modbus Organization
October 24, 2006
http://www.Modbus.org
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MODBUS MESSAGING ON TCP/IP IMPLEMENTATION GUIDE
V1.0b
CONTENTS
1 INTRODUCTION ........................................................................................................... 2
1.1 OBJECTIVES ....................................................................................................... 2
1.2 CLIENT / SERVER MODEL................................................................................... 2
1.3 REFERENCE DOCUMENTS ................................................................................. 3
2 ABBREVIATIONS .......................................................................................................... 3
3 CONTEXT ..................................................................................................................... 3
3.1 PROTOCOL DESCRIPTION ................................................................................. 3
3.1.1 General communication architecture ......................................................... 3
3.1.2 MODBUS On TCP/IP Application Data Unit ............................................... 4
3.1.3 MBAP Header description ......................................................................... 5
3.2 MODBUS FUNCTIONS CODES DESCRIPTION .................................................... 6
4 FUNCTIONAL DESCRIPTION........................................................................................ 7
4.1 MODBUS COMPONENT ARCHITECTURE MODEL............................................... 7
4.2 TCP CONNECTION MANAGEMENT ....................................................................10
4.2.1 Connections management Module............................................................10
4.2.2 Impact of Operating Modes on the TCP Connection..................................13
4.2.3 Access Control Module ............................................................................14
4.3 USE of TCP/IP STACK ........................................................................................14
4.3.1 Use of BSD Socket interface ....................................................................15
4.3.2 TCP layer parameterization.....................................................................18
4.3.3 IP layer parameterization .........................................................................19
4.4 COMMUNICATION APPLICATION LAYER...........................................................20
4.4.1 MODBUS Client .......................................................................................20
4.4.2 MODBUS Server......................................................................................26
5 IMPLEMENTATION GUIDELINE ...................................................................................32
5.1 OBJECT MODEL DIAGRAM ................................................................................32
5.1.1 TCP management package ......................................................................33
5.1.2 Configuration layer package.....................................................................35
5.1.3 Communication layer package..................................................................36
5.1.4 Interface classes......................................................................................37
5.2 IMPLEMENTATION CLASS DIAGRAM.................................................................37
5.3 SEQUENCE DIAGRAMS......................................................................................39
5.4 CLASSES AND METHODS DESCRIPTION ..........................................................42
5.4.1 MODBUS Server Class ............................................................................42
5.4.2 MODBUS Client Class..............................................................................43
5.4.3 Interface Classes.....................................................................................44
5.4.4 Connexion Management class..................................................................45
