This code will find the available COM ports on your computer.


==================================================
Option Explicit

'API Declarations
Public Declare Function CreateFile Lib "kernel32.dll" 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.dll" (ByVal hObject As Long) As Long

'API Structures
Public Type SECURITY_ATTRIBUTES
nLength As Long
lpSecurityDescriptor As Long
bInheritHandle As Long
End Type

'API constants
Public Const FILE_SHARE_READ = &H1
Public Const FILE_SHARE_WRITE = &H2
Public Const OPEN_EXISTING = 3
Public Const FILE_ATTRIBUTE_NORMAL = &H80


'Module

'Return TRUE if the COM exists, FALSE if the COM does not exist
Public Function COMAvailable(COMNum As Integer) As Boolean
Dim hCOM As Long
Dim ret As Long
Dim sec As SECURITY_ATTRIBUTES

'try to open the COM port
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
'close the COM port
ret = CloseHandle(hCOM)
End If
End Function

'Usage:
Sub Command1_Click()
Dim i As Integer

For i = 1 To 16
If COMAvailable(i) Then
MsgBox "COM" & i & " OK", vbInformation
Else
MsgBox "COM" & i & " Not OK", vbExclamation
End If
Next
End Sub