> Joe I am not really looking for the physical layer, I sort of have that, > Chris is actually very close to what I am looking for. Apologies if I > haven't described the problem correctly Hi Luis, I just gave a couple of examples of the micro-sensor interface. Obviously that is only part of the system. Developing the method and s/w took a lot longer than designing a few PCBs. What Chris described is very similar to my implementation, except I use assembler. The nett result is that the core knows at all times what is connected (h/w is Plug And Play / hot- swappable) and what the functions and ranges of each module are. The modules can also talk to each other BTW and execute some simple commands without further instruction from the core, but do report their activity to it Joe --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .