Modbus 485 Communication In Case of 2 or more Masters/Clients

Question

I am curruntly working on building industrial application. I have a Slave - PCB device built on STM32 that gets data from the sensors. It transfers serial data in every 5 seconds through RS485 USB Converter to the Master A, according to the Master A's request. Now, I want to add another Master B using RS485 Converter to LAN. In this case, how can I avoid data corruption or collisions when both masters try to read data simultanously.

[***A PCB Slave includes Modbus RS485 library which means it sends serial data.]

RS485 Converter to LAN (Converter that I am using) -> http://www.realsys.co.kr/goods/content.asp?guid=581&cate=367&params=cate=367^sword=^swhat=^listsort=favorite^listtype=album^listsize=5^page=

More clearly, I want to read data from PCB Slave using two masters. One is using RS485 RTU USB Converter and the other one is using RS485 Converter to TCP/IP. Is it possible to communicate smoothly in this scenario without interruptions or data corruption?

WHY I need to use 2 Masters: Because, we have already built the product using Master A (using USB Converter). It is already installed on the places. Now, some customers want to get the same product plus, the option for Master B (Modbus TCP/IP). By using Master B, they want to get sensors data to their own industrial PC using LAN.

I have set hardware parts and used some logic to test the case. When both masters tried to read data at the same time I am getting Timeout Error from the Master that uses USB Converter. The other Master is throwing the following Exception error:

Exception - System.IO.IOException: Unable to read data from the 
transport connection: A blocking operation was interrupted by a 
call to WSACancelBlockingCall. ---> 
System.Net.Sockets.SocketException: A blocking operation was 
interrupted by a call to WSACancelBlockingCall
at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, 
Int32 size, SocketFlags socketFlags)
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 
offset, Int32 size)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 
offset, Int32 size)
at FluentModbus.ModbusTcpClient.TransceiveFrame(Byte 
unitIdentifier, ModbusFunctionCode functionCode, Action`1 
extendFrame)in 
/home/runner/work/FluentModbus/FluentModbus/src/FluentModbus/Client/ModbusTcpClient.cs:line 269
   at FluentModbus.ModbusClient.ReadInputRegisters(Byte unitIdentifier, UInt16 startingAddress, UInt16 quantity) in /home/runner/work/FluentModbus/FluentModbus/src/FluentModbus/Client/ModbusClient.cs:line 317
   at FluentModbus.ModbusClient.ReadInputRegisters[T](Int32 unitIdentifier, Int32 startingAddress, Int32 count)

Answer 1

You can't put multiple masters on a serial line. You need a different hardware setup where you put a Modbus TCP to RS485 Gateway (not a dumb serial to ethernet converter) in front of the serial line, and then both masters need to use Modbus TCP to talk to the Gateway.