Problem reading half-duplex virtual serial port with SerialPort cl

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

I am using the new SerialPort class to read from several different pieces of
hardware. I have gotten it to work with devices that conect using both real
and virtual serial ports, but I have a piece of hardware that the serialport
object isn't working for.

The non-working device is a barcode scanner that has a USB connection and a
virtual serial port driver. The driver says it is only half duplex, so that
may be the problem. I downloaded a utility program that monitors serial port
traffic, and it can see the data coming in just fine, however when I try to
read using the SerialPort object I get the following error:

IOException was caught

The I/O operation has been aborted because of either a thread exit or an
application request.

Since I was able to get it to work with other devices, I suspect the problem
is with this particular device, probably the driver being half duplex. Are
there settings I can use to overcome this?
 
Hi,

Half-duplex is not the issue. What this means is that the device only sends
data, it does not receive data from your application. So, anything that you
might send will be ignored.

That isn't the issue.
The I/O operation has been aborted because of either a thread exit or an
application request.
<<

This normally means that there has been a DataReceived event (and a Read or
ReadExisting call, for example) AFTER the port has been closed. The only
time that I have seen this error is when the application is exited (and the
port has been closed), but data is sent by the connected device BEFORE the
SerialPort object has been disposed. I presume that this isn't the
situation that you are seeing?

Can you try something for me to see if this really is a device-specific
issue. Please download the VS2005 terminal example from my homepage. Even
though it has been written in VB, the issues will be the same for C#. Run
it with your device, select the required port, open it and generate a scan.
Let me know the result.

Dick

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.
 
Your program reads the scanner perfectly. I am not sure what I am doing
wrong, I just open the serialport object and call readline or readbyte and it
crashes. I get the error on two different computers. I will look at the
code again, but I'm not doing anything too complicated so I don't know whats
happening. As I said before, I use the same method for reading other pieces
of hardware and it works just fine.
 
I figured out how to get it to work. I was just calling readline or readbyte
whenever I wanted to wait for something to come across the port, which
apparently worked for some devices. However the better way is to have a
function handle the serialport's datarecieved event and read the data inside
the handler function.

Thanks for your reply, the serial monitor code on your website was extremely
helpful.

Nate
 
Hello! I got the same problem as yours, I have no idea with it. Could you help me please?

Imports System
Imports System.Data
Imports System.Windows.Forms
Imports System.IO
Imports System.IO.Ports

Public Class Form1

Dim WithEvents port As New IO.Ports.SerialPort("COM1", 9600, Parity.None, 8, StopBits.One)

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Try
port.ReceivedBytesThreshold = 1
If port.IsOpen = True Then
port.Close()
End If
port.Open()
lblError.Text = "COM1 port connected!"
lblError.ForeColor = Color.Green
TextBox1.Text = "0.000kg"
Catch ex As Exception
lblError.Text = ex.Message
End Try
End Sub

Private Sub port_DataReceived1(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles port.DataReceived
Try
TextBox1.Invoke(New myDelegate(AddressOf updateTextBox), New Object() {})
Catch ex As System.IO.IOException
MsgBox(ex.Message)
End Try

End Sub

'------------------------------------------------------
' Delegate and subroutine to update the Textbox control
'------------------------------------------------------
Public Delegate Sub myDelegate()
Public Sub updateTextBox()
Dim tmpStr As String
Dim pos As Integer
tmpStr = Trim(port.ReadLine)
pos = InStr(tmpStr, "GS")
If pos > 0 Then
tmpStr = Trim(Mid(tmpStr, pos + 2))
If tmpStr <> Trim(TextBox1.Text) Then
With TextBox1
.Text = tmpStr
'.ScrollToCaret()
End With
End If

End If
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
port.Close()
Me.Close()
End Sub
End Class
 
Back
Top