Erik

Thanks for the reply, I was going to use an external 555 to act as a missing bit timer, when no data was on the line then it would time out after a reasonable period (2-5mSecs) and give an output(OK to TX) if data kept coming thru then this would reset the timer (/OKtoTX) If I did it like this the likelyhood of 2 devices on the network TXing at the same time would be pretty small I spose that this relates to earlangs and other traffic loadings but you can see the theory - Any thoughts?

Thanks

Marshall