Opto 22 industrial Ethernet controllers can act as Modbus Master or Modbus Slave or both on either serial and/or Ethernet networks. And because the master also has an IP address rather than just an ID, the Modbus/TCP system could also support multiple masters too! As there a more addresses available to devices when using Ethernet networks, the Modbus/TCP protocol provides for an increased number of slaves. 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. There, however, can only be one master in such a network. In a Modbus RTU serial connection, there can be up to 255 slaves each identified with their unique ID. Modbus Masters and Modbus SlavesĪs with most communication protocols, there are generally Slaves (Servers) and Masters (Clients) and Modbus is no exception.
Modbus RTU being used for serial connections using RS232, RS422 or RS485 and Modbus/TCP using standard Ethernet cabled networks. 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 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.Īs 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 is a serial protocol language originally introduced by Modicon in the late 1970’s for use in its programmable logic controllers.
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