Encountered an Issue with reconnecting to the Service

[CLST-Isopp]

I was wondering if reconnection with the NModus Service is supported as I tried to reconnect but the system keeps throwing me exception errors regarding the socket.

Exception thrown: 'System.Net.Sockets.SocketException' in System.dll
Exception thrown: 'System.IO.IOException' in System.dll
Exception thrown: 'System.IO.IOException' in NModbus.dll

Maybe I'm implementing it wrong?

[MPapst]

• Can you open a plain socket to your target system on the specified port?
• When does that happen? when connecting or during the connection?
• Can you copy the complete exception message?

[CLST-Isopp]

So I might have been unclear. The connection works fine the first time. So yes i can open the socket I can open the connection and everything is working perfectly. When I pull the network cable from the SPS-Modul I'm connected too, using TCP-IP it throws the above mentioned errors. But when I try to reconnect, plugging the SPS-Modul back into the PC. It cannot recreated the connection and continously throws the above mentioned errors.

System.Net.Sockets.SocketException (0x80004005): No connection could be made because the target machine actively refused it 127.0.0.5:502 at System.Net.Sockets.TcpClient..ctor(String hostname, Int32 port)

I Provide you with the NModbus part implementation. Maybe you can point me towards the mistake?

    TcpClient client;
    IModbusMaster master;
    ModbusFactory factory;
    string ipAdresseSave;
    int portSave;
    public bool ModbusTcpMasterConnection(string ipAdress, int port)
    {
        
        if (client == null)
        {
            client = new TcpClient();
            ipAdresseSave = ipAdress;
            portSave = port;
        }
        client = new TcpClient(ipAdress, port);            
        factory = new ModbusFactory();
        master = factory.CreateMaster(client);
        client.ReceiveTimeout = 5000;
       
        return client.Connected;
    }

    public void ReadValues(ref byte[] data)
    {
        if (client.Connected)
        {
            ushort startAddress = 1504;
            ushort numInputs = 9;
            ushort[] values = master.ReadHoldingRegisters(1, startAddress, numInputs);                
            Buffer.BlockCopy(values, 0, data, 0, values.Length * 2);
        }            
        ModbusTcpMasterConnection(ipAdresseSave, portSave);
    }

[MPapst]

Try against a Server program on a Desktop Computer.
You can use Ananas64 for example.

I‘ve seen a lot of modbus implementations, especially on PLC devices that are not clearing a socket when the client is disconnected.

Can you reconnect after a while (an hour or so)?