Master and slave in MODBUS RTU communication?
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The data in the PLC needs to be transmitted via MODBUS RTU to the DCS system screen for display; so which one is the master station, the DCS or the PLC? Which one is the slave station? How are the master station and slave station defined? Can either one be chosen as the master and the other as the slave? Also, can MODBUS RTU communicate in both directions? Currently, the data from the PLC is displayed in the DCS. Is it possible to also display the data from the DCS on the PLC? Is it still necessary to run an additional network cable, using separate ports on the PLC and DCS to achieve this?
The slave station is passive; data is placed there for the master station to read from and write to, and it does not send data to the master station on its own. The master station is proactive; it can retrieve the data it needs from the slave stations and can also modify the data on those slave stations. You yourself said that MODBUS is bidirectional – over a single wire, the master station can both send and receive data. But it certainly won’t be at the same time.
Through the Modbus protocol, the DCS displays data from the PLC, and the PLC also displays data from the DCS. . Of course it’s possible~ DCS uses the MODBUS master mode to read data from PLCs, and it is also possible to write DCS data into PLCs. No additional interfaces are required. . . But you should figure out how many commands are needed to complete one poll, to see if the timing meets the requirements: lol
The master station is the requester, while the slave station is the responder; DCS acts as the master station and enables two-way communication without the need for additional wiring
The data in the PLC needs to be transmitted via MODBUS RTU to the DCS system screen for display; so which one is the master station, the DCS or the PLC? Which one is the slave station? Depending on the device’s capabilities, many DCS/PLC products can function either as a master or as a slave. How are the master station and slave station defined? Can either one be chosen as the master and the other as the slave? See the above answer. Also, can MODBUS RTU communicate in both directions? Currently, the data from the PLC is displayed in the DCS. Is it possible to also display the data from the DCS on the PLC? Is it still necessary to run an additional network cable, using separate ports on the PLC and DCS to achieve this? Yes. Sure. No additional wiring is required.
Typical instruments are designed as slave devices, waiting for the master device to poll them. The master device is usually a device for centralized display, and it can collect data from multiple slave devices (instruments) via a bus for processing.