Question Working with RS232 serial port

bjfguitar · #1 (**permalink**) 07-08-2009, 1:34 AM

First of all I want to apologise for only signing up to ask for help, but I've been debugging, experimenting and searching for days for a solution to this problem. Posting is always the last resort.

I'm not very experienced with Visual Basic, although I am proficient in a variety of languages. I got asked to create a program for my fathers product that connects to it to read and write information.

I am using Visual Basic 2008 Express, and to connect I'm using the Serial Port class. I have everything working fine, but the problem is, every time I try to read data from it (with the Read function) the program crashes.

I wrote my own code at first, but through the debugging I decided to just download a pre-made code which I found and modify it to what I need.

Code:

Public Class Form1
    Dim WithEvents serialPort As New IO.Ports.SerialPort

    Private Sub Form1_Load( _
       ByVal sender As System.Object, _
       ByVal e As System.EventArgs) _
       Handles MyBase.Load

        For i As Integer = 0 To _
           My.Computer.Ports.SerialPortNames.Count - 1
            cbbCOMPorts.Items.Add( _
               My.Computer.Ports.SerialPortNames(i))
        Next
        btnDisconnect.Enabled = False
    End Sub

    Private Sub DataReceived( _
       ByVal sender As Object, _
       ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) _
       Handles serialPort.DataReceived
        Dim rcvBuf(1024) As Byte
        serialPort.Read(rcvBuf, 0, rcvBuf.Length)
        'txtDataReceived.Invoke(New myDelegate(AddressOf updateTextBox), New Object() {})
    End Sub

    Private Sub btnSend_Click( _
       ByVal sender As System.Object, _
       ByVal e As System.EventArgs) _
       Handles btnSend.Click
        Try
            Dim xmtBuf() As Byte = {&H96, &H1, &H50, &H51, &H74}
            serialPort.Write(xmtBuf, 0, xmtBuf.Length)
            With txtDataReceived
                .SelectionColor = Color.Black
                .AppendText(txtDataToSend.Text & vbCrLf)
                .ScrollToCaret()
            End With
            txtDataToSend.Text = String.Empty
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try

    End Sub

    Public Delegate Sub myDelegate()
    Public Sub updateTextBox()
        With txtDataReceived
            .Font = New Font("Garamond", 12.0!, FontStyle.Bold)
            .SelectionColor = Color.Red
            .AppendText(serialPort.ReadExisting)
            .ScrollToCaret()
        End With
    End Sub

    Private Sub btnConnect_Click( _
       ByVal sender As System.Object, _
       ByVal e As System.EventArgs) _
       Handles btnConnect.Click
        If serialPort.IsOpen Then
            serialPort.Close()
        End If
        Try
            With serialPort
                .PortName = cbbCOMPorts.Text
                .BaudRate = 96000
                .Parity = IO.Ports.Parity.None
                .DataBits = 8
                .StopBits = IO.Ports.StopBits.One
                ' .Encoding = System.Text.Encoding.Unicode
            End With
            serialPort.Open()

            lblMessage.Text = cbbCOMPorts.Text & " connected."
            btnConnect.Enabled = False
            btnDisconnect.Enabled = True
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub
End Class

Thankyou to anyone who can help me!
Ben.

Robert_Zenz · #2 (**permalink**) 07-08-2009, 8:09 AM

Hello.

What does this device send, and do you have to send a command so that it does it?

Bobby

bjfguitar · #3 (**permalink**) 07-08-2009, 10:11 AM

Hey Robert, thanks for the reply.

I send a hex code:
Dim xmtBuf() As Byte = {&H96, &H1, &H50, &H51, &H74}
serialPort.Write(xmtBuf, 0, xmtBuf.Length)

Which translates out to 96 01 50 51 74

The device I'm writing to reads this function and will respond as a hex as well, which I'm trying to read here:
Dim rcvBuf(1024) As Byte
serialPort.Read(rcvBuf, 0, rcvBuf.Length)

Thanks,
Ben.

Robert_Zenz · #4 (**permalink**) 07-09-2009, 4:25 AM

Does this reply always have a fixed length? If yes, you can set ReceivedBytesThreshold-Property to that value, so that the Received event will only fire if all data has arrived.

Quote:

Which translates out to 96 01 50 51 74

We are still talking about Hex-Values and not Decimal-Values, do we?

Try This:

Code:

    Private Sub DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles serialPort.DataReceived
        Dim rcvBuf(Me.serialPort.ReadBufferSize) As Byte
        Dim read As Integer = Int32.MinValue

        read = Me.serialPort.Read(rcvBuf, 0, rcvBuf.Length)

        Dim res As New StringBuilder()

        For i As Integer = 0 To read Step 1
            res.Append(rcvBuf(i).ToString("X2"))
        Next

        Debug.Print(res.ToString())
    End Sub

This should print every received data to the Debug-Window.

Bobby

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