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Check whether a serial or parallel port is available
[ All Languages » VB »  Windows]

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The Open statement also supports special device names such as COM1 or LPT2. You can build on this feature and use the Open command to test whether a given serial or parallel port is available. Here are two functions that perform this task:

Click here to copy the following block
' Check whether a given COM serial port is available

Function IsComPortAvailable(ByVal portNum As Integer) As Boolean
  Dim fnum As Integer
  On Error Resume Next
  fnum = FreeFile
  Open "COM" & CStr(portNum) For Binary Shared As #fnum
  If Err = 0 Then
    Close #fnum
    IsComPortAvailable = True
  End If
End Function

' Check whether a given LPT parallel port is available

Function IsLptPortAvailable(ByVal portNum As Integer) As Boolean
  Dim fnum As Integer
  On Error Resume Next
  fnum = FreeFile
  Open "LPT" & CStr(portNum) For Binary Shared As #fnum
  If Err = 0 Then
    Close #fnum
    IsLptPortAvailable = True
  End If
End Function

You can use the above function also for determining how many serial or parallel ports are installed, using a loop:

Click here to copy the following block
Dim count As Integer, i As Integer
For i = 1 To 16
  If IsComPortAvailable(i) Then count = count + 1
Next
MsgBox "Found " & count & " serial ports"


Submitted By : Nayan Patel  (Member Since : 5/26/2004 12:23:06 PM)

Job Description : He is the moderator of this site and currently working as an independent consultant. He works with VB.net/ASP.net, SQL Server and other MS technologies. He is MCSD.net, MCDBA and MCSE. In his free time he likes to watch funny movies and doing oil painting.
View all (893) submissions by this author  (Birth Date : 7/14/1981 )


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