Public Function CommOpen(intPortID As Integer, strPort As String, _
                         strSettings As String) As Long

  Dim lngStatus As Long
  Dim udtCommTimeOuts As COMMTIMEOUTS

  On Error GoTo Routine_Error

  ' See if port already in use.
  If udtPorts(intPortID).blnPortOpen Then
    lngStatus = -1
    With udtCommError
      .lngErrorCode = lngStatus
      .strFunction = "CommOpen"
      .strErrorShift = "Port in use."
    End With
  Else
    ' Open serial port.
    udtPorts(intPortID).lngHandle = CreateFile(strPort, GENERIC_READ Or _
                                                        GENERIC_WRITE, 0, ByVal 0&, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)

    If udtPorts(intPortID).lngHandle = -1 Then lngStatus = SetCommError("CommOpen (CreateFile)")
  Else
    udtPorts(intPortID).blnPortOpen = True

    ' Setup device buffers (1K each).
    lngStatus = SetupComm(udtPorts(intPortID).lngHandle, 1024, 1024)

    If lngStatus = 0 Then
      lngStatus = SetCommError("CommOpen (SetupComm)")
    Else
      ' Purge buffers.
      lngStatus = PurgeComm(udtPorts(intPortID).lngHandle, PURGE_TXABORT Or _
                                                           PURGE_RXABORT Or _
                                                           PURGE_TXCLEAR Or _
                                                           PURGE_RXCLEAR)

      If lngStatus = 0 Then
        lngStatus = SetCommError("CommOpen (PurgeComm)")
      Else
        ' Set serial port timeouts.
        With udtCommTimeOuts
          .ReadIntervalTimeout = -1
          .ReadTotalTimeoutMultiplier = 0
          .ReadTotalTimeoutConstant = 1000
          .WriteTotalTimeoutMultiplier = 0
          .WriteTotalTimeoutMultiplier = 1000
        End With

        lngStatus = SetCommTimeouts(udtPorts(intPortID).lngHandle, udtCommTimeOuts)

        If lngStatus = 0 Then
          lngStatus = SetCommError("CommOpen (SetCommTimeouts)")
        Else
          ' Get the current state (DCB).
          lngStatus = GetCommState(udtPorts(intPortID).lngHandle, _
                                   udtPorts(intPortID).udtDCB)

          If lngStatus = 0 Then
            lngStatus = SetCommError("CommOpen (GetCommState)")
          Else
            ' Modify the DCB to reflect the desired settings.
            lngStatus = BuildCommDCB(strSettings, udtPorts(intPortID).udtDCB)

            If lngStatus = 0 Then
              lngStatus = SetCommError("CommOpen (BuildCommDCB)")
            Else
              ' Set the new state.
              lngStatus = SetCommState(udtPorts(intPortID).lngHandle, udtPorts(intPortID).udtDCB)

              If lngStatus = 0 Then
                lngStatus = SetCommError("CommOpen (SetCommState)")
              Else
                lngStatus = 0
              End If
            End If
          End If
        End If
      End If
    End If
  End If
End If

CommOpen = lngStatus
Exit Function

Routine_Error:
lngStatus = Err.Number
With udtCommError
  .lngErrorCode = lngStatus
  .strFunction = "CommOpen"
  .strErrorShift = Err.Description
End With
CommOpen = lngStatus
End Function