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General Category => Do-more CPUs and Do-more Designer Software => Topic started by: Controls Guy on October 29, 2024, 02:35:32 PM

Title: Trouble with Modbus RTU over 485 to Siemens V20
Post by: Controls Guy on October 29, 2024, 02:35:32 PM

I'm having trouble polling from a BRX to a Siemens V20 over 485.   .XferCount increments but no values are written to the target range in BRX (I can even overwrite registers in range, so I know it's not just writing zeros).  I can communicate from a laptop to the V20 via FTDI USB-485 adaptor, and I get good non-zero data.

I tried running a PC Modbus slave and letting the BRX target the PC, and I never get an RX light on the PC from the BRXs TX nor an RX light on the BRX indicating a response.

Port setup:  9600-O-8-1 (tried both terminated and not)

Anyone successfully do this?

Title: Re: Trouble with Modbus RTU over 485 to Siemens V20
Post by: BobO on October 29, 2024, 03:26:32 PM

Don't have the Siemens thing, but I went between two BRX -18s. RS485, 9600-8-1-O. Read 10 holding registers. Write to N0. Worked perfectly first time. Not sure what to suggest.