The Sales department thinks we should develop PCI card solution to supply RS-485 and work as the first door controller on the network.

Do they use Patriot missiles when they go sparrow hunting?

RS-485 cards are availble from many suppliers for very little money, or you can use a B&B 232 to 485 converter. Even better get a USB to 485 external converter.

A card access system to a door, best guess, will fit in a 4k '51, which then can feed a PC with 'who entered'

Erik