Electronic – Modbus RTU over RS232 link

armlpc1768modbusrs232rs485

I am designing a convertor board that will interface three device with Modbus RTU RS232 port to a Modbus RTU RS485 network.
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Slaves supports Modbus RTU, but their ports is different from master port.

The ARM processor is intended to handle the communications of master RTU with different devices in the different addresses.
I konw the packet structure in the Modbus RTU protocol is as follows:
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The question is: After receiving master packet and finding out the destination device (by reading slave ID byte), what should i send to the Device? Should i send the same packet that i received from master ? does it need to manipulate something (slave ID,…) within packet?

Thanks in advance

Best Regards

Best Answer

After implementing the whole system and some try and error, i figured out that we must pass the packet through unmodified. RS232 RTU device will ignore the Slave ID filed in the packet.

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