There are two types of Modbus serial protocols, RS-232 and RS-485. This flexibility is part of the lasting appeal of Modbus. Modbus data can be carried on two channels - over serial communication, or over a network connection. Two Channels: Modbus RTU vs Modbus TCP/IP If your monitoring device needs information to present to a human operator, the targeted device will read holding registers to receive the data. Manufacturers are free to use any number of formats (Modbus function code fields) to suit the function of their devices. That's really all holding registers are, and you'll configure an RTU to only collect data from the registers you want. For simplicity's sake, imagine a database or a spreadsheet with two columns: one column contains the register name, and the other column contains the register value. A register could contain one analog value, a collection of binary values, or something else. Devices store important values of different data types in various 16 bit registers. A remote terminal unit (RTU) is also able to tell a Modbus device when and what commands to execute.Įven the format of the data is flexible. A system will consist of an RTU which polls (or interrogates) a device for data and alarm information. Like most remote monitoring system protocols, Modbus follows the master/slave model, but the devices are typically referred to as interrogators/responders, respectively.

It's a polled protocol, where a central master asks each device for status information in a sequential loop.įor devices with large numbers of input registers (more than a few hundred), you'll benefit from a master device that can prioritize more important registers over less important ones.

It moves raw words and bits, and it has very few restrictions.

There is no need to learn and deploy other protocols. It might require just a matter of days to implement, which can save months of work.

It uses a simple message structure, making it less difficult to deploy.

It can be included in a wide range of device types from any equipment vendor. It's used extensively for a number of its key benefits, including the following: Modbus communication protocol is a widely used protocol in Supervisory Control and Data Acquisition ( SCADA) systems. It's now widely used for connecting many types of industrial electronic devices on different types of networks.

It was developed in 1979 for use with Programmable Logic Controllers ( PLCs). Modbus is a communications protocol for transmitting data between two or more devices. Understanding Modbus Protocol - RTU vs TCP vs ASCII

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