Modbus Specifications
MODBUS is an application-layer messaging protocol, positioned at level 7 of the OSI model. It provides client/server communication between devices connected on different types of buses or networks.
The de facto industrial serial standard since 1979, MODBUS continues to enable millions of automation devices to communicate. Today, support for the simple and elegant structure of MODBUS continues to grow. The Internet community can access MODBUS at a reserved system port 502 on the TCP/IP stack.
MODBUS is a request/reply protocol and offers services specified by function codes. MODBUS function codes are elements of MODBUS request/reply PDUs. This protocol specification document describes the function codes used within the framework of MODBUS transactions.
This document is the Modbus application protocol V1.1b3. It describes the function codes used within the framework of MODBUS transactions.
The Modbus Security protocol provides protection through the blending of Transport Layer Security (TLS) with the traditional Modbus protocol. TLS encapsulates Modbus packets to provide authentication and message-integrity protection. The new protocol also leverages X.509v3 digital certificates for authentication of the Server and Client. The new Modbus Security protocol uses port 802.
MODBUS Over Serial Line FOR LEGACY APPLICATIONS ONLY
This is the obsolete Modbus specification from 1996. Use only to address legacy issues. Please do not use it for new implementations.
Modbus Serial Line Protocol and Implementation Guide V1.02 Please use this for new MODBUS implementations.
The MODBUS Messaging Implementation Guide version 1.0b was provided by Schneider Automation. The objective of this document is to provide reference information for software developers implementing the MODBUS messaging service. This document gives an accurate and comprehensive description of a MODBUS messaging service implementation. Its purpose is to facilitate interoperability between devices using the MODBUS messaging service. The encoding for all MODBUS function codes is not described in this document. For this information please refer to the MODBUS application protocol specification.
The MODBUS Messaging Implementation Guide contains three parts:
- Overview of MODBUS over TCP/IP
- Functional description of a MODBUS client, server and gateway implementation
- MODBUS implementation example that proposes the object model
Object Messaging Specification for the Modbus TCP Protocol
An object messaging protocol for use with Modbus TCP, used as a component in the SEMI sensor bus Network Communication Standard (NCS).