Thank you for the link to the sample C code and the explanation. All my code is written in VB.NET 2008. I have many years experience with it from my previous business dealings before I retired and the program was going before I thought too much about it. I have got the 3 wire interface running really well and the 9 bit data word was a real challenge especially in VB.NET, I think the hardest part was getting the half clock cycle delay correct during the bus turn around.
Strange, but I think I saw some source code on the german site modul-bus ag (or so), where they sell a silabs chip on a usb-bridge.