Great ideas and I appreciate the discussion. I understand the 'random' addressing of the IO boards on the chain but for my project I HAVE to have them in a linear order. For example: the 1st board is 1024, 2nd board is 1040, the 3rd board is 1056, etc. This is because I have to know what the address is of the outputs and the inputs on the board (there are 16 each).

The addressing rotary switch idea will work but then if I forget to address a board or if I quickly address it, there will be conflicts on the bus.
An idea I have been working is if I have a 485 network in half-duplex mode (less bus collisions), but have 2 serial channels on each IO board. The Master talks to the 1st board via the 485-IN, then the 'chain' continues to the next board by going out a 485-OUT which is connected to the next board and so on.
For the hardware I plan on using an 18F part

The MASTER will initiate a command and the 1st board in the chain will answer, get its address unless it already has one, and then merely acts as a forwarding node on the chain.
This looks like it will work but my question now is at what latency cost? I have successfully driven the 485 at 57.6K but it will take some CPU time to read in the packet and transmit it back out on the chain.
This method while adding network latency, does overcome the total number of slaves on the network as each IO board starts over <grin>.

Criticisms or comments? Any further thoughts?