gpl11 – http://www.dsvendinginc.com/pdf-manuals/gpl11.pdf
http://www.monstervending.com/manualspdf/food/FoodKing-Setup-4290001.pdf
What does the serial port do, and what can it be made to do?
http://en.wikipedia.org/wiki/Multidrop_bus
http://www.google.com/patents/US20030149827
High voltage, have to figure that out.