Vending: Frequently Asked Questions



Communication interfaces

Communication with a vending machine

Reading audit data of a vending machine


As BonusData AG gets a lot of questions every day, concerning vending and vending machines, we decided to publish a page on this subject. As we just started this page,   the contents isn't very big yet. But in the next weeks we will continue to add new items.

Communication interfaces

Today's modern vending machines with electronic vending machine controllers (VMC) will usually support two interfaces.

1. The first interface to communicate with the payment system internally of the vending machine:

Interface: Hardware: Protocol / Published:
Executive 20 mA current loop Executive Protocol 'A' issued by Mars Electronic International.
BDV 20 mA current loop BDV001 Specification issued by the BDV Committee.
MDB Multi Drop Bus Multi Drop Bus issued by NAMA and EVA, originally by CoinCo Inc. USA.

This interfaces are not true 20mA current loop interface as familiar in the industry, but rather a current sensitive serial link. The interfaces in this table are the mainly used communication interfaces inside vending machines. There are still some others, but we will just focus on the most important.

2. The second interface to communicate with the outside world, e.g. reading out of audit data:

Interface: Hardware: Protocol / Published:
EVA-DTS wired Audio-Jack 6.3 mm DDCMP protocol with EVA-DTS contents on 9600 Baud.
EVA-DTS infrared Infrared DDCMP protocol with EVA-DTS contents on 2400 Baud.
DEX/UCS wired Audio-Jack 6.3 mm DEX/UCS protocol with EVA-DTS contents on 9600 Baud.
EVA-DTS IrDa Standard IrDa New, DDCMP protocol with EVA-DTS contents up to 115200 Baud.

The interfaces are not always true RS-232, many devices just have a 5V TTL level signal. Also here are other proprietary protocols on the market but we focus on the most common standards.

Communicating with a vending machine

The communication with the vending machine must be quite fast to gain reasonable reactions when the user interacts with the machine. Short data frames are send periodical with an interval of 40 to 200 ms. Participants are Change-Giver, Bill-Acceptors, Card-Readers e.t.c. The concept is a master-slave with one master and one or more slaves.

Following table shows an overview of the possible configurations:

Protocol: Master: Poll interval: Number of slaves:
Executive Payment-System 40ms Max. 5, VMC, Card-Reader, Audit-Unit.
BDV Payment-System 100ms Max. 5, VMC, Card-Reader, Audit-Unit.
MDB VMC 50-200ms Max. 5, Change-Giver, Card-Reader, Bill-Acceptor, Audit-Unit.

As all this serial communication links are current sensitive, it's not possible to connect it direct with a standard RS-232 interface of PC. BonusData AG developed special interface cable to communicate with a vending machine through a standard serial RS-232 interface.

Available PC cables:

BD-2003 MDB-Master if the PC is master against the MDB-Bus. Power supply BD-1003 is recommended.

BD-2010 MDB-Slave if the PC is slave against the MDB-Bus. Power supply is not required. Note: With the standard Windows applications it's not possible to act as slave, because the response time of MDB with 4 ms can not be achieved.   

Reading audit data of a vending machine

The readout of audit data is not time critical. Here are different criteria's to consider. In praxis, the operator will use some kind of a handheld terminal to collect the audit data. In the praxis, vending machines will have very different behaviors depending on the brand of the vending machine.

You will be confronted with following problems:

To solve this kind of problems, BonusData AG developed an audit data cable that normalizes the electrical levels to standard RS-232. Further the interface cable can be turned ON/OFF by use of the RTS signal to simulate plug and unplug. This enables the possibility to permanent connect a device without disturbing the vending machine or Change-Giver.

BD-2007 audit data cable with converter will solve most of described problems. A power supply isn't necessary.

Anyway, there are also some vending machines with a absolute normal behavior, where you may readout the audit data at anytime with a straight cable without an interface.

This may explain the use of special interface cable generally to communicate with a vending machine and readout of audit data.

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