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What is Baudrate in a Modbus RTU network?
The Modbus RTU (Remote Terminal Unit) protocol is widely used in the HVAC industry and in industrial automation systems for communication between devices. Baudrate, in the context of Modbus RTU communication, refers to the speed at which data is transmitted over the communication network.
For example, if a communication channel has a baudrate of 19.200, it means that there are 19.2000 signal changes per second. However, the actual data transfer rate may differ depending on the encoding scheme used. For instance, if each signal change represents one data bit, the bits per second (bps) would also be 19.200. But if the encoding scheme allows multiple bits to be transmitted per signal change, the bps can be higher than the baudrate.
Baudrate in Modbus RTU communication is important because it affects the speed, synchronization, transmission distance, interference resistance, and device compatibility. Selecting an appropriate baudrate is crucial to ensure reliable and efficient communication between Modbus devices. On a Modbus RTU network all devices must be set at the same baudrate, otherwise communication between devices will be impossible. The default setting of all our devices is 19.200 and we advise on NOT changing this parameter.
The baudrate plays a crucial role in Modbus RTU communication for the following reasons:
1. Data Transmission Speed: Baudrate determines how quickly data can be transmitted between devices. It represents the number of signal changes per second and is measured in bits per second (bps). A higher baudrate allows for faster data transmission, enabling more efficient communication between devices.
2. Synchronization: Baudrate ensures synchronization between the transmitting and receiving devices. Both devices must operate at the same baudrate to ensure that they understand and interpret the transmitted data correctly. If the baudrate is mismatched, data corruption or communication errors may occur.
3. Transmission Distance: The choice of baudrate also depends on the distance between the devices. Higher baudrates are suitable for shorter distances because the signal quality can deteriorate over long distances, leading to errors. Lower baudrates are often used for longer distances to maintain reliable communication.
4. Interference and Noise: Baudrate can affect the resistance of the system to electrical interference and noise. Higher baudrates are more susceptible to noise and interference, potentially leading to data errors. In such cases, using a lower baudrate can help improve the system's reliability in noisy environments.
5. Device Compatibility: The baudrate used in Modbus RTU communication must be supported by both the transmitting and receiving devices. It is important to ensure that the devices involved can operate at the selected baudrate. Some devices may have limitations on the supported baudrates, so compatibility should be verified before establishing communication.
In order to ensure reliable connection and communication between the devices on a Modbus RTU network, their baudrate has to be the same (the factory setting is 19.200).
In summary, the baudrate in Modbus RTU communication is important because it affects the speed, synchronization, transmission distance, interference resistance, and device compatibility. Selecting an appropriate baudrate is crucial to ensure reliable and efficient communication between Modbus devices.
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