Modbus.Net TcpClient fails exactly every 6th poll

Question

I implemented a Modbus.Net v1.4.3 client and poll data peridoically in a main program and experience strange behaviour.

Every 6th poll gives:

  Data = null
  Success = false
  ErrorCode = 0
  ErrorMsg  = ""

The other polls work just fine.

Feel free to blaim my code along the way.

In the following code only this line does the poll :

//Get data from machine
var result = await _machine.GetMachineMethods<IMachineMethodDatas>().GetDatasAsync(MachineDataType.CommunicationTag);`

Modbus Client class:

using Microsoft.Extensions.Logging;
using Modbus.Net;
using Modbus.Net.Modbus;

/// <summary>
/// Modbus using Modbus.Net
/// </summary>
internal class ModbusClient
{
    public ModbusClient(string ip, byte id, List<AddressUnit<int, int, int>> addressConfig)
    {
        // init machine object with address-unit config
        _machine = new ModbusMachine<int, int>(id, ModbusType.Tcp, ip, addressConfig, true, id, 0, 2);
    }

    /// <summary>
    /// Modbus.Net Machine
    /// </summary>
    private IMachineProperty<int> _machine;

    /// <summary>
    /// Poll configured addresses.
    /// </summary>
    /// <returns>Collection of <see cref="ReturnUnit{TReturn}"/></returns>
    /// <exception cref="IOException">Poll failed.</exception>
    public async Task<ICollection<ReturnUnit<double>>> PollReturnUnits()
    {
        //Get data from machine
        var result = await _machine.GetMachineMethods<IMachineMethodDatas>().GetDatasAsync(MachineDataType.CommunicationTag);

        //Error handling
        if (result.Datas is null || !result.IsSuccess)
        {
            throw new IOException($"code:{result.ErrorCode}, msg:{result.ErrorMsg}");
        }
        //Return AdressUnits
        return result.Datas.Values;
    }
}

Edit:

-Please don't rely on the documentation of the package, since it's outdated. Download package and paste my code to browse.

-The GetDatasAsync reads some configured registers. It returns a "ReturnStruct" with the properties (which partly have wrong plural): Datas, Success, ErrorMsg, ErrorCode.

Answer 1

I have tested the slave with this Modbus Scanner: https://store.chipkin.com/products/tools/cas-modbus-scanner

With an hour of observation I was able replicate the behaviour, altough it occours, that it's much less frequent with the scanner, which lead me to blame the modbus library first.

I guess thats it for this question. Thanks to everyone!