The Industrial Raspberry Pi Forum

Posted: **07 Mar 2025, 19:21**

Hi all,

back with a new problem.
I have a service written in C# that reads RS-485 inputs from a UHF receiver.
It is using OSDP protocol, so I am sending Poll frames and reading the subsequent replies.

The point is: if I am using Windows and my PC (AMD Ryzen processor), connected with a USB/RS485 cable, everything works flawlessly.
Bringing the same exact service on the Connect 4.... the replies start to be completely nonsense.

I checked a thousand times the cables, redone multiple times from the scratch, redone by an electrician.

Nothing different... I am sending a correct Poll frame and receiving garbage.

There is something I must to on the RevPi in order to enable or configure the RS-485 port?

thankssss

Ciao
Gabriele

Posted: **07 Mar 2025, 20:39**

Hi Gabriele,

maybe you can share a simplified example of your code so we can have look. First thing which comes to my mind: Correct RTS pin handling on the RS485 interface. If you use the serial interface in rs485 mode the serial subsystem should have all steps. If you're not using the interface in rs485 mode try to activate it.

Nicolai

Posted: **10 Mar 2025, 15:16**

Hi Nicolai,

this is the main "loop":

Code: Select all

        private void PollReader(object state)
        {
            _pollingTimer.Change(Timeout.Infinite, Timeout.Infinite);
            try
            {
                lock (_lock)
                {
                    byte readerAddress = 0x00; // Reader address

                    byte sequenceNumber = _sequenceNumber;
                    _sequenceNumber = (byte)((_sequenceNumber < 7) ? _sequenceNumber + 1 : 5); // Cycle between 5, 6, 7

                    byte[] pollFrame = BuildPollFrame(readerAddress, sequenceNumber);

                    SendFrame(pollFrame);

                    byte[] response = ReceiveFrame();
                    if (response != null)
                    {
                        ParseResponse(response).GetAwaiter();
                    }
                }
            }
            catch (Exception e)
            {
                _hdLogger.WriteLog(e.Message).GetAwaiter();
                _logger.LogError(e.Message);
            }
            finally
            {
                _pollingTimer.Change(TimeSpan.FromMilliseconds(_readInterval), TimeSpan.FromMilliseconds(_readInterval));
            }
            
        }

... and this is the definition of the serial port object

Code: Select all


            _serialPort = new SerialPort(portName, baudRate, parity, dataBits, stopBits)
            {
                ReadTimeout = 2000,
                WriteTimeout = 500
            };

... and this is the various values:

portName = "/dev/ttyRS485"
baudRate = 9600
parity = Parity.None
dataBits = 8
stopBits = StopBits.One

... and with the same configuration it works properly on Windows, while in the RevPi OS I don't have a proper answer when I try to read the reply after I send the POLL frame.

The wiring has been redone multiple times, by two different people, and we tried with and without the GND pin connected.

I really can't get an angle.......

The Industrial Raspberry Pi Forum

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