Code:
...
Declare Function OPENCOM Lib "Port" (ByVal A$) As Integer
Declare Sub CLOSECOM Lib "Port" ()
Declare Sub RTS Lib "Port" (ByVal b%)
...

Private Sub Form_Load()
i = OPENCOM("COM1,9600,N,8,1")
If i = 0 Then MsgBox ("Schnittstelle nicht verfügbar!")
End Sub

...
RTS 1
DELAYUS (10)
RTS 0
DELAYUS (10)
RTS 1
...
So etwa?

Blackbird