Serial port dropping data with Readline()

Question

I am using serial port to read the data off the scale that is attached to the thin client. In 99% of cases the data is read correctly - ie whatever is on the scale is what is captured by the application. However, sometimes, it looks like data is dropped. For instance instead of 90.007 it will be read as 0.007. I am using ReadLine function:

private void CaptureWeight()
    {
         globalCounter++;
         string value = "";
         _sp.DiscardInBuffer();

          while (!this._processingDone)
          {
              try
              {                     

                  value = this._sp.ReadLine();                      

                  if (value != "")
                  {
                      if (value == "ES")
                      {
                          _sp.DiscardInBuffer();
                          value = "";
                      }
                      else
                      {
                          this.Invoke(this.OnDataAcquiredEvent, new object[] { value });
                      }
                  }
              }
              catch (TimeoutException)
              {
                  //catch it but do nothing
              }
              catch
              {
                  //reset the port here?
                  MessageBox.Show("some other than timeout exception thrown while reading serial port");
              }
          }
    } //end of CaptureWeight()

Answer 1

When does "ES" come? It is theory possible that the value immediately after "ES", is not read correctly, because you call DiscardInBuffer(). If in that time the buffer contains part of the next reading, e.g. the 9 in 90.007, the 9 gets discarded and you read 0.007.

Try discarding only everything before the last CR LF. But leave incomplete lines.

Answer 2

Don't call DiscardInBuffer. The operating system buffer is filled asynchronously as data is shifted in through the UART. Read all of the data and act on it accordingly because you have no way of knowing what is in the buffer at the time you discard it!