Multi-drop bus

The Multi-Drop Bus is a vending machine interface that is required to connect coin changers , banknote readers or even cashless payment systems. It is used z. B. in beverage or cigarette machines .

function

The standard was issued by the American National Automatic Merchandising Association and defines both the physical interface (electrical specifications) and the communication process between the participants.

Communication is based on the master / slave principle. All slaves are connected to the Master-Transmit with optocouplers . All slaves are connected in parallel to Master-Receive via an open collector circuit and again galvanically isolated by means of an optocoupler. The transfer rate is 9600  bd and 32 slaves can be addressed. The master polls the slaves, which prevents collisions in the bus .

literature

• AF Benner, M. Ignatowski, JA Kash, DM Kuchta, MB Ritter: Exploitation of optical interconnects in future server architectures . In: IBM Journal of Research and Development . tape 49 , no. 4.5 , July 2005, p. 755–775 , doi : 10.1147 / around 494.0755 ( HTML version from March 14, 2008 ( memento from March 14, 2008 in the Internet Archive ) in the Internet Archive).
• National Automatic Merchandising Association (Ed.): Multi-Drop Bus / Internal Communication Protocol - MDB / ICP , Version 3.0, March 26, 2003 ( Memento of July 5, 2010 in the Internet Archive ).
• National Automatic Merchandising Association (Ed.): Multi-Drop Bus / Internal Communication Protocol - MDB / ICP , Version 4.2, February, 2011 ( Memento of October 12, 2018 in the Internet Archive ).