Serial Communications

I am having similar problems as several other postings I've read here concerning reading from serial ports in Visual basic 2005 Express. Unfortunately I have not seen an answer.
- I can build a list of available com ports
- I can write data to a com port using the "How to: Send Strings to Serial Ports in Visual Basic "
- I cannot read from the port using the sample code for "How to: Receive Strings From Serial Ports in Visual Basic"
I have narrowed the line in question to

Dim Incoming As String = com1.ReadLine()

By setting

com1.ReadTimeout = 8000

If after the timeout I open Hyperterminal and open the port, all of the data that should was sent is received. I am connected to another computer using a null modem cable with hyperterminal on the other end to send the data that should be received. The code is below. Basically I have a form with a button that starts the sub procedure to read the port. I've added a line after the open to write to the serial port first ,just to be sure the port is open and hyperterminal on the other computer receives the output, but when I type or send a file back, my VB program still times out(i've set the timeout long enough to send data). Any help would greatly be apreciated since I've already burned a day and 1/2 on this.
Thanks,
Harry
== code ===
Private Sub ButtonSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonReceive.Click
    Dim trans As String = "test"
   'trans = readport("COM1", 9600, 0, 8, 1)
    trans = readport("COM1")
   RichTextBox1.Text = trans
End Sub

Private Function readport(ByVal portName As String, Optional ByVal baudRate As Integer = 9600, Optional ByVal parity As System.IO.Ports.Parity = 0, Optional ByVal dataBits As Integer = 8, Optional ByVal stopBits As System.IO.Ports.StopBits = 1)
' Receive strings from a serial port.
Dim returnStr As String = ""
Dim value As Integer
    Using com1 As IO.Ports.SerialPort = _
            My.Computer.Ports.OpenSerialPort(portName, baudRate, parity, dataBits, stopBits)
      value = com1.ReadTimeout
      com1.ReadTimeout = 8000
      'SerialPort.InfiniteTimeout - consider later
        Do
            com1.WriteLine("First Write then read") 'writes fine
            ' Dim Incoming As String = com1.ReadLine()
            Dim Incoming As String = com1.ReadChar() 'timeout
              'open Hyperteminal and all data is read from buffer that should have been read above
              MsgBox("After Read") 'never see this
            If Incoming Is Nothing Then
              MsgBox("incoming is nothing") ' never see this
              Exit Do
            Else
                returnStr &= Incoming & vbCrLf
            End If
        Loop
    End Using
    Return returnStr
End Function

Answer this question

Serial Communications

nolla

Usually when I do serial communications, I set up an event handler for the comm port's data received event. Then I get the data whenever it comes in and usually will resend my output until I get a response or send it too many times, at which point I timeout, close the port, and raise a timeout event. The code could look something like this:

Dim WithEvents port As New SerialPort("COM1")

Private Sub SendData(ByVal data As String)
    If Not port.IsOpen Then port.Open()
    port.Write(data)
End Sub

Private Sub port_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles port.DataReceived
    If e.EventType <> SerialData.Chars Then Exit Sub

    Dim inData As String = port.ReadExisting
    'process incoming data here
End Sub

RoshanShah

There is a fairly clear discussion on this in the Help area of VB 2005 titled
"How to: Make Thread-Safe Calls to Windows Forms Controls"

I setup a simple sub routine to display all my serial port communications, then just call it and pass what I want displayed. In the sample code below, my subroutine is DislayText and my text form field is StatusTextbox

Dim inData As String = comport.ReadExisting ' read the data

DisplayText(inData) ' use threadsafe way to write to StatusTextbox

' This method demonstrates a pattern for making thread-safe TextBox Displays
Private Sub DisplayText(ByVal [text] As String)
' InvokeRequired required compares the thread ID of the
' calling thread to the thread ID of the creating thread.
' If these threads are different, it returns true.

If Me.StatusTextbox.InvokeRequired Then
   Dim d As New SetTextCallback(AddressOf DisplayText)
   Me.Invoke(d, New Object() {[text]})
Else
   Me.StatusTextbox.Text += [text]
End If
End Sub

Hope this helps
Harry

omegarazor
My problem is solved. You would think after all these years in the business and working with serial communications I would have figured it out in 5 minutes, but no I had to waste 2 days missing the obvious. The answer was as simple as enabling dtr. I discovered this by adding a "Serial Port Component Control" to my form from the Toolbox and checking the properties. Seeing dtrenable, I enabled it and instantly the data started flowing. This setting is obviously turned on in a terminal program such as Hyperterminal and that should have been my big clue why it worked and mine didn't. I hope this helps anyone else as dense as me in solving their problem.

The key line I needed to get it working was

com1.DtrEnable = True ' com1 is my serial port connection from the DIM line

Thanks again for your help and the code for event handling, it works great.
Harry
Charles Washika
I've copied your code exactly but when I try to run it I get the error...

Cross-thread operation not valid: Control 'RichtextBox1' accessed from a thread other than the thread it was created on.

How can I get the serial port event handler to update the "richtextbox1" with the data from the serial port

StoneWasHere

Thanks for the quick reply. I've played with your suggestion for quite a while. I really like the idea of the even handler being triggered on serial data received, I'll need that for the application I am developing. Unfortunately, it never triggers and in fact the buffer doesn't appear to be read. After exiting my program, I open hyperterminal and out comes all the data I tested with. I believe I have all the code correct. Is there a chance there is something amiss with the VB 2005 express io.ports buffer read

The only success I have had so far is finding a comport.exe download in an article titled "COM Port Sample" located in help that uses win32 api calls. Far messier than it looks like it has to be, but at least I am getting some data. I still would rather get it to work either your way or the snippet way in my earlier post, there just doesn't appear to be anything obvious I am doing wrong. Below is the code I used from your recommendation. I put in several test points to display ports being open or closed and a reset button if it is closed, but otherwise the same. Is there another part of the handler I am missing

Thanks Again
Harry

Imports System.Text
Imports System.IO.Ports
Public Class Form1

Dim WithEvents com1 As New SerialPort("COM1")

Private Sub Form1_load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Try
        com1.Open()
    Catch ex As Exception
        RichTextBox1.Text = "Port is closed, please check and retry" + vbCrLf
    End Try
    If com1.IsOpen Then
        RichTextBox1.Text = "port is open" + vbCrLf
    End If
End Sub
Private Sub port_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles com1.DataReceived
    MsgBox("made it to sub data received")
    If e.EventType <> SerialData.Chars Then Exit Sub
    Dim inData As String = com1.ReadExisting
    'process incoming data here
    RichTextBox1.Text += inData + vbCrLf
End Sub

Serial Communications

Answer this question

Serial Communications

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Serial Communications

Serial Communications

nolla

RoshanShah

omegarazor

Charles Washika

StoneWasHere