List of products by brand Modbus

Modbus is an industrial protocol that was developed in 1979 to make communication possible between automation devices. Originally implemented as an application-level protocol intended to transfer data over a serial layer, Modbus has expanded to include implementations over serial, TCP/IP, and the user datagram protocol (UDP). This document provides an in-depth view of the protocol implementation.

Modbus is a request-response protocol implemented using a master-slave relationship. In a master-slave relationship, communication always occurs in pairs—one device must initiate a request and then wait for a response—and the initiating device (the master) is responsible for initiating every interaction. Typically, the master is a human machine interface (HMI) or Supervisory Control and Data Acquisition (SCADA) system and the slave is a sensor, programmable logic controller (PLC), or programmable automation controller (PAC). The content of these requests and responses, and the network layers across which these messages are sent, are defined by the different layers of the protocol.