1. Status of this specification








télécharger 102.36 Kb.
titre1. Status of this specification
page1/7
date de publication03.07.2017
taille102.36 Kb.
typeDocumentos
  1   2   3   4   5   6   7
OPEN MODBUS/TCP SPECIFICATION

Release 1.0, 29 March 1999


Andy Swales

Schneider Electric

aswales@modicon.com

Contents





Contents 2

1. Status of this specification 3

2. Overview 3

3. Conformance class summary 5

4. Protocol structure 7

5. Protocol reference by conformance class 8

6. Exception codes 17

Appendices 18

A. Client and Server Implementation Guidance 18

B. Data Encoding for non-word data 21



1. Status of this specification



Initial release 3 Sept 1997
Draft for public review.
Re-release 29 March 1999 at Revision 1.0.
No technical changes, clarifications only.

Added Appendices A and B in response to common implementation questions.

This specification of MODBUS/TCP is being published by being publicly visible on the World Wide Web. It is intended for the benefit of developers wishing to use MODBUS/TCP as an interoperability standard in the field of industrial automation.
Since MODBUS and MODBUS/TCP are in reality ‘de-facto’ standards, in that many vendors and products implement it already, this specification primarily explains the specific encoding of MODBUS messages over the TCP communication protocol universally available on the Internet.


2. Overview



MODBUS/TCP is a variant of the MODBUS family of simple, vendor-neutral communication protocols intended for supervision and control of automation equipment. Specifically, it covers the use of MODBUS messaging in an ‘Intranet’ or ‘Internet’ environment using the TCP/IP protocols. The most common use of the protocols at this time are for Ethernet attachment of PLC’s, I/O modules, and ‘gateways’ to other simple field buses or I/O networks.
The MODBUS/TCP protocol is being published as a (‘de-facto’) automation standard. Since MODBUS is already widely known, there should be little information in this document which could not be obtained elsewhere. However, an attempt has been made to clarify which functions within MODBUS have value for interoperability of general automation equipment, and which parts are ‘baggage’ from the alternate use of MODBUS as a programming protocol for PLC’s.
This is done below by grouping supported message types into ‘conformance classes’ which differentiate between those messages which are universally implemented and those which are optional, particularly those specific to devices such as PLC’s.

2.1 Connection-oriented



In MODBUS, data transactions are traditionally stateless, making them highly resistant to disruption from noise and yet requiring minimal recovery information to be maintained at either end.
Programming operations, on the other hand, expect a connection-oriented approach. This was achieved on the simpler variants by an exclusive ‘login’ token, and on the Modbus Plus variant by explicit ‘Program Path’ capabilities which maintained a duplex association until explicitly broken down.
MODBUS/TCP handles both situations. A connection is easily recognized at the protocol level, and a single connection may carry multiple independent transactions. In addition, TCP allows a very large number of concurrent connections, so in most cases it is the choice of the initiator whether to reconnect as required or re-use a long-lived connection.
Developers familiar with MODBUS may wonder why the connection-oriented TCP protocol is used rather than the datagram-oriented UDP. The main reason is to keep control of an individual ‘transaction’ by enclosing it in a connection which can be identified, supervised, and canceled without requiring specific action on the part of the client and server applications. This gives the mechanism a wide tolerance to network performance changes, and allows security features such as firewalls and proxies to be easily added.
Similar reasoning was used by the original developers of the World Wide Web when they chose to implement a minimal Web query as a single transaction using TCP on well-known port 80.

  1   2   3   4   5   6   7

similaire:

1. Status of this specification iconNote de l’auteur de la spécification : Cette spécification comprend...

1. Status of this specification iconDoucet Hennessy Association Granted Charitable Status

1. Status of this specification iconSetting up in business demarrer une entreprise legal status

1. Status of this specification iconSpécification fonctionnelle et d’architecture

1. Status of this specification iconLivrable a : Spécification des Services Web d’Import et d’Export de Dossiers

1. Status of this specification iconSpecification technique generale des transformateurs de distribution triphases a l’huile

1. Status of this specification iconSpécification du diffuseur flexible fdd
«Standard Method of Test for Surface Burning Characteristics of Building Materials and Assemblies»

1. Status of this specification iconJob Description and Person Specification
«Performances» pour les activités de Simulation, et apporte son support au btm durant les offres

1. Status of this specification iconNotes de Cours Algorithmes et Structures de Données usto lmd s3-S4
«la spécification d’un schéma de calcul, sous forme d’une suite d’opérations élémentaires obéissant à un enchaînement déterminé»....

1. Status of this specification iconNotes de Cours Algorithmes et Structures de Données usto lmd s3-S4
«la spécification d’un schéma de calcul, sous forme d’une suite d’opérations élémentaires obéissant à un enchaînement déterminé»....








Tous droits réservés. Copyright © 2016
contacts
ar.21-bal.com