The REAL problem with PC to multi is that the PC does not provide 485. How ever excellent the converters from B&B (or is it B B) Electronics are, this is still patchwork. The right solution is to make or buy a 485 card for the PC. I have in the past made several such, my way is to put as many '51s as needed (in one case I had 3 to handle the amount of traffic required) on the card and use dual port memory to interface to the PC bus. The above case was an industrial knitting machine with 48 '51s mounted on the machine, eash controlling 8 pins, all controlled from the PC.

Have fun,

Erik