MDB/ICP is a standard used for the perpherals of vending machine, like Coin Acceptor/Changer or Bill Validator/Recycler, etc. In fact, MDB is just a 9600bps UART but in 9bit mode, so you can't connect it to PC directly. The code running in a AVR mcu, it preprocess some low level MDB protocol, and give you other UART to PC, you can control it easily then.