The basic Modbus commands can instruct an RTU to change the value in one of its registers, control or read an I/O port, and command the device to send back one or more values contained in its registers. All Modbus commands contain checksum information to allow the recipient to detect transmission errors. Only the intended device will act on the command, even though other devices might receive it (an exception is specific broadcastable commands sent to node 0, which are acted on but not acknowledged). A Modbus command contains the Modbus address of the device it is intended for (1 to 247). On Ethernet, any device can send out a Modbus command, although usually only one master device does so (Modbus TCP/IP will be supported by Vutlan in the coming future). In serial and MB+ networks, only the node assigned as the Master may initiate a command. Modbus messages are framed (separated) by idle (silent) periods Communications and devicesĮach device intended to communicate using Modbus is given a unique address. A Modbus RTU message must be transmitted continuously without inter-character hesitations. Modbus RTU is the most common implementation available for Modbus. The RTU format follows the commands/data with a cyclic redundancy check checksum as an error check mechanism to ensure the reliability of data. Modbus RTU - This is used in serial communication and makes use of a compact, binary representation of the data for protocol communication. Protocol versionsĪt the moment Vutlan supports the following Modbus versions: Modbus enables communication among many devices connected to the same network, for example, a system that measures temperature and humidity and communicates the results to a controller/monitoring unit. Moves raw bits or words without placing many restrictions on vendors. The main reasons for the use of Modbus in the industrial environment are:ĭeveloped with industrial applications in mind, Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices. Modbus is a serial communications protocol.

Modbus rtu serial communication protoco