In the moment there are two UDF's for serial communication:
>Serial Port / COM Port UDF (needs comMG.dll)
>Serial Communication using kernel32.dll
The first UDF is very popular, but it has the disadvantage, that an unknown DLL needs to be used.
The second UDF use the Windows API, but it has much less features.
So, I decided to create an another UDF for my requirements.
You can find the result here: http://www.autoitscript.com/wiki/CommAPI
It is a further development of the se