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:

' Check whether a given COM serial port is availableFunction 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 IfEnd Function' Check whether a given LPT parallel port is availableFunction 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 IfEnd Function

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

Dim count As Integer, i As IntegerFor i = 1 To 16    If IsComPortAvailable(i) Then count = count + 1NextMsgBox "Found " & count & " serial ports"