Multidrop bus
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This article is about the vending machine protocol. For the network topology, see Network_topology#Bus.
See also: ccTalk
The MDB protocol is used in vending machines to interconnect different modules (such as bill acceptors, card readers and coin changers). The physical connection is realized as an unmodulated serial Bus with the data rate fixed to 9600 baud, and 9 bits in each data word transmitted.
MDB has evolved as a standard protocol after 1995, allowing alternative (e.g. Smartcard based) payment systems to be connected to existing vending machines.
Bus addressing is based on the device type, which allows for a very simple protocol stack as no initial enumeration needs to be performed, but has the disadvantage that only one device of each type can be attached.
