I am writing a VB.Net (VS 2015) application to control equipment in real time which is connected via USB ports. The equipment requires that text string, terminated by a chr(13) be sent. Most commands will get a response back. For example one command (set VALVE1 ON) will open a valve one on the equipment. When plugging the equipment in it appears as COM7 on my laptop, though I can change this via device manager, and have done so to ensure I don't get the problem just on COM7. the euipment then sends back a string to confirm valve has opened. A light also displays to show valve has opened.

When running my code the valve opens and about seven seconds later the coms port closes and the equipment locks up. If I use Hyperterminal or Docklight to send the string, then valve opens and string comes back.

I started using Framework 4.5 and the valve would not open. I now use Framework 4.6.1 and get the results described.

If I connect to another computer running Hyperterminal or Docklight then the sent string is displayed correctly and strings can be sent back to my application.

 Sub SendSerialData(ByVal data As String)
        ' Send strings to a serial port.

        Dim _continue As Boolean
        Dim s As String
        Dim sl As Integer
        Dim rct As Integer
        Dim CC As Integer
        Dim incoming As String

        Dim J As Integer
        J = 0
        Dim jl As Integer
        Dim bytes() As Byte

        ' Dim ascii As New ASCIIEncoding()

        ' Create two different encodings.
        Dim ascii As Encoding = Encoding.UTF8

        Dim unicode As Encoding = Encoding.Unicode

        ' Convert the string into a byte array.
        Dim unicodeBytes As Byte() = unicode.GetBytes(data)

        ' Perform the conversion from one encoding to the other.
        Dim asciiBytes As Byte() = Encoding.Convert(unicode, ascii, unicodeBytes)

        ' Convert the new byte array into a char array and then into a string.
        Dim asciiChars(ascii.GetCharCount(asciiBytes, 0, asciiBytes.Length) - 1) As Char
        ascii.GetChars(asciiBytes, 0, asciiBytes.Length, asciiChars, 0)
        Dim asciiString As New String(asciiChars)

        Dim indata As String

        ' Send strings to a serial port.
         ' sending one bit at a time. Have also tried whole line at a time.

        Using com1 As IO.Ports.SerialPort = My.Computer.Ports.OpenSerialPort("COM7", 115200, Parity.None, 8, StopBits.One)

            com1.NewLine = Chr(13)
            jl = Len(data)
            Dim b As Byte

            For J = 0 To Len(asciiChars) - 1
            Next j


            _continue = True

            s = ""
            sl = 0
            rct = 0
            While _continue
                CC = 0
                    While com1.BytesToRead = 0 And CC < 2000
                        CC = CC + 1
                        J = com1.BytesToRead
                    End While
                Catch ex As Exception
                    _continue = False
                End Try

               incoming = com1.ReadExisting

                rct = rct + 1
                If rct > 100 Then _continue = False

                s = s & incoming

                If Len(s) >= 1 Or rct > 1000 Then
                    _continue = False
                    sl = Len(s)


                    '    MsgBox(Len(s) & "  -" & s)
                End If
            End While
        End Using

        MsgBox(rct & " - " & s & "  Length " & sl)

    End Sub

So has anyone had this problem and found a solution please ? I suspect it is something to do with Framework, because one version would not work and current one partially works. So far no strings returned.

Alternatively can any one point me to sending strings to USB without using Framework please ?

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All 3 Replies

Sorry for the delay. But let's tackle a few items.

To do this without .NET you'll have to use a language other than VB.net, C# and so on. But I don't see any reason to avoid .NET here.

-> Now to work. There are so many code examples on the web for serial IO in VB.net that I suggest you try a terminal program from source to see how that works.

What I think I see is an old school polling the serial port method. You may have to up your game here to have a routine that fires on serial reception and be careful not to send data and have no delay for the response.

Example that I find doesn't work in psuedo code.
1. Open port.
2. Send string.
3. Wait for answer.

What's wrong with that? Not much. But we are dealing with the real world and I've been burned by drivers and devices that take one hundred milliseconds for the port to get ready. I can't write what your choice would be here but for many years I'll open the port early then the user can click on this or that button. The human's delay has always been long enough to avoid that old issue.

BTW, my other nice trick is to scan the ports for a connection so the user never has to tell me which COM port to use. I find that end users today are very unaware of old school serial ports.


Thank you for your suggestions.

I have tried much of what you have suggested, so I apologose for having said so.

I have tried various opening and sending strings, including having a message box between opening the port and sending the string, for the reasons you say.

I also have a routine for scanning and finding the ports, but for testing this bit I know what the com port numbber is..

Have you sucessfully used Framework 4.5 and/or 4.6 to communicate with a port ?

Since posting I have downloaded a port monitor which appears to show my program continuing to send data. I am investigating further. I have also heard indirectly from the board makers who say I can't lock the board from VB.....

Well, no. My apps on on .NET 3.5 for long reasons. They were fielded back in 2009 and I leave them be for reasons.

One of the test tools I used along the way was a serial sniffer. This can be a hardware box ($$$$) or cheap cables wired up to listen on TX or RX on a second PC. That way we see what's on the wire.

I have fielded serial port comms for well, since DOS days. The code above is pretty rudimentary but what is this about lock up? If you exit your app and open a terminal, is it still locked up?

Also, if you are in the USA or Can, drop me a direct line about the app you need.

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