Need info on MPI Bus Siemens S7

I was searching the net for info on the Siemens S7 MPI bus but didn't find anything really usefull. has some nice info, but
it is not accurate enough to make my own driver software (although it should be possible by re-making 'nodave' a freeware MPI driver).
I want to make a driver in Delphi. I know of several commercial products, but I want to be able to distribute my software as freeware...
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