Re:Positional/physical addressing

I have a large group (hundreds) of switches and displays.Their state needs to be determined/updated rather slowly(a few hertz).  Each has local smarts so it can retainsome state information and processing capability.Their physical arrangement varies from one installation tothe next.  So, there is no economy of scale available by"settling" on a specific configuration or physical arrangement.I would like to be able to address them (the entire *set*) -- andpass data to/fro -- with a small, fixed number of conductors /havingbuilt them all identically/.  The amount of data exchanged beingtraded off vs.  update rate for a given interface bandwidth.The obvious "one wire" scheme would have a gazinta and cumzoutafor each device so the device could modify a serial bit streamto account for its "position" in that stream.I can pipeline processing between devices so the overall accessrate remains high (though latency obviously suffers).But, a single device failure renders all downwind devicesinaccessible (or, possibly ALL devices, depending on implementation)I'm looking at a two wire solution that piggybacks the datastream on power and ground (those "two wires").  But, itadds complexity to the devices (I want to keep them REALLYsmall and dirt cheap)Any existing schemes that allow this without the failure mode cited?