Modbus and Modbus Protocol

Modbus is a serial protocol language originally introduced by Modicon in the late 1970’s for use in its programmable logic controllers. Modbus developed a name for its reliability and started to be adopted as the standard protocol in most industrial hardware systems, including those of Opto 22.

As industrial controls systems became more advanced and serial communications between devices required more data and quicker transfer speeds, the industrial take up of Ethernet communication led to the provision of the Modbus protocol that worked over a standard Ethernet network.

Modbus RTU and Modbus/TCP Protocols

The serial version of the Modbus protocol is widely known as Modbus RTU and its Ethernet version known as Modbus/TCP to distinguish between the two. Modbus RTU being used for serial connections using RS232, RS422 or RS485 and Modbus/TCP using standard Ethernet cabled networks.

Modbus Masters and Modbus Slaves

As with most communication protocols, there are generally Slaves (Servers) and Masters (Clients) and Modbus is no exception. In a Modbus RTU serial connection, there can be up to 255 slaves each identified with their unique ID. There, however, can only be one master in such a network.

In Modbus/TCP, the protocol evolved to incorporate the use of standard IP addressing rather than ID’s but some Modbus/TCP systems still employ both addresses. As there a more addresses available to devices when using Ethernet networks, the Modbus/TCP protocol provides for an increased number of slaves. And because the master also has an IP address rather than just an ID, the Modbus/TCP system could also support multiple masters too!

Opto 22 industrial Ethernet controllers can act as Modbus Master or Modbus Slave or both on either serial and/or Ethernet networks. This provides an extremely versatile industrial hardware controllers that has the ability to talk multiple industrial protocol language as well as Modbus all at the same time. These units could be used as:

  • Modbus RTU to Modbus/TCP protocol converters
  • Serial to Ethernet protocol converters
  • Multiple slave and master configuration
  • Gateways between protocols such as BACNet, EtherNet IP, DeviceNet, Profibus, HART, etc.

The areas we cover include but not exclusive to are:

  • Modbus I/O
    • Our Modbus I/O solutions range from stand alone DIN rail devices to rack mount high density and support either Modbus Slave or Modbus Master configuration for distributed and local I/O systems.
      • Low cost programmable logic controller with Modbus RTU support
      • Modbus Digital I/O for DIN rail mounting
      • Modbus Analogue I/O for DIN rail mounting
      • High Density Modbus Digital and Analogue I/O
  • Modbus Human Machine Interfaces
    • We offer a complete and competitive range of Modbus enabled colour touch screens or HMI’s.
      • HMI’s from 4.3” up to 10” colour touch screens providing Modbus communication and many other protocols for PLC systems such as Opto 22, Siemens, Allen Bradley, Mitsubishi, Omron, WAGO, Beckoff, etc.
      • 7” and 10” colour touch screens providing low cost human machine interface for Modbus Serial and/or Ethernet systems.
  • Modbus Protocol Converters/Data Servers
    • Whether you need a device that converts Modbus Serial to Modbus TCP, we provide a diverse range of product solutions to accomplish the task.
      • RS232/RS422/RS485 to Ethernet Modbus devices
  • Modbus Concentrators
    • Our experience in Modbus communications has enabled us to provide solutions to the majority of our customer communications projects. These have range from simple Modbus mapping between two or more systems, up to solutions which provide multiple Modbus connections via serial and/or Ethernet.
      • Programmable Automation Controllers, PAC’s provide industrial Modbus communications between single or multiple systems
      • PAC’s support multiple protocols such as Ethernet/IP, DNP3, Modbus, BACNET, SNMP, SMTP and others.

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