Multidrop bus
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A multidrop bus (MDB) is a computer bus in which all components are connected to the same set of electrical wires. A process of arbitration determines which device gets the right to be the sender of information at any point in time. The other devices must listen for the data that is intended to be received by them.
Multidrop buses have the advantage of simplicity and extensibility, but electronically are limited to around 200–400 MHz (because of reflections on the wire from the printed circuit board (PCB) onto the die) and 10–20 cm distance (SCSI-1 has 6 metres). Multidrop standards such as PCI are therefore being replaced by point-to-point systems such as PCI Express.
Multidrop buses are also used by vending machine controllers to communicate with the vending machine's components, such as a currency detector (coin or note reader). Not surprisingly, these MDB buses communicate with the MDB protocol, a 9-bit serial protocol.
[edit] MDB in Vending Machines
MDB is utilized in Vending machines to connect the Bill Acceptors and Coin Changer mechanisms. This evolved as the standard in vending machines after 1995.
With this innovation, the vending machine industry also failed to be able to arbitrate multiple devices on one bus (i.e. 3 Bill Acceptors and 2 coin mechanisms). Hence, it is only possible to put 1 MDB compliant Bill Acceptor and 1 MDB compliant coin mechanism in 1 or a series of vending machines.
