How to implement Modbus write request during polling function

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C#

Hi all,

I am implementing Modbus communication using .net 2010 using c# as coding. I have achieved polling technique with help of the code available from this website only. So as of now polling process is going on well, but the problem is when i send write requests to a particular slave polling stops or hangs the UI. So how to proceed for write function in Modbus. The following is my code.

private void btnTest_Click_1(object sender, EventArgs e)
       {                    
           if (flagtest == 0)
           {
                   ushort start = 0;
                   short[] value = new short[1];                

                   try
                   {
                       while (!mb.SendFc06(SlvID1, start, (ushort)2, value)) ;
                   }
                   catch (Exception err)
                   {
                       DoGUIStatus(Error in write function:err.Message);
                   }
                 
                   btnTest.BackgroundImage = global::AnnunciatorMonitoringTool.Properties.Resources.lightbulb;
                  
                   flagtest = 1;
           }
           else
           {
               flagtest = 0;
               btnTest.BackgroundImage = global::AnnunciatorMonitoringTool.Properties.Resources.lightbulb_off;
              
           }

The problem is whenever i click on the btntest button during polling process to perform some action, the polling process completely stops or sometimes the write request is sent to slave & response is also obtained. But after this the polling doesn't continue. Why is that happening..? How do i send write requests safely to slaves & get response from it & also continue with polling..?