Hola
Creo que esto te puede ayudar:
creas un modulo clase e insertas el siguiente codigo, claro como para hacerlo mas comodo..
Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, lpSecurityAttributes As SECURITY_ATTRIBUTES, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Public Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Public Type SECURITY_ATTRIBUTES
nLength As Long
lpSecurityDescriptor As Long
bInheritHandle As Long
End Type
Public Const FILE_SHARE_READ = &H1
Public Const FILE_SHARE_WRITE = &H2
Public Const OPEN_EXISTING = 3
Public Const FILE_ATTRIBUTE_NORMAL = &H80
'// Retorna TRUE si el puerto existe o esta disponible, FAlse en otro caso
Public Function COMAvailable(COMNum As Integer) As Boolean
Dim hCOM As Long
Dim ret As Long
Dim sec As SECURITY_ATTRIBUTES
hCOM = CreateFile("\.\COM" & COMNum & "", 0, FILE_SHARE_READ + _
FILE_SHARE_WRITE, sec, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)
If hCOM = -1 Then
COMAvailable = False
Else
COMAvailable = True
ret = CloseHandle(hCOM)
End If
End Function
y luego para comprobar un puerto este seria un ejemplo que rellena un combobox con los puertos disponibles:
For i = 1 To 16
If COMAvailable(i) Then
cboComm.AddItem "COMM" & i
End If
Next
Saludos