Vending Machine/Cashless Device

The MDB spec already takes into account cashless devices, so we simply have to build a device that conforms to the spec.

The specification defines 3 levels of cashless devices, with more more features the higher the level. The Vending Machine (VMC) also has a level, and a device and VMC can only communicate using the highest commonly supported level. As our VMC is only level 1, we only need to implement a level 1 cashless device.

So let's look at what a level 1 device needs to do. Here we will reference commands by their plain English names. For the technical details on these commands, please refer to the specification section 7. For details on how these commands are sent/received by the VMC, refer to secitons 2,3 and 4.

A (slightly simplified) diagram of the state machine, with commands sent from/to the VMC in capitals.

The cashless device ( is basically a state machine with 5 states (7 for level 2 and 3 machines). These states are:

1. Inactive
2. Disabled
3. Enabled
4. Session Idle
5. Vend

When turned on, the cashlss device enters state 1. Almost all state transistions are initiated by the VMC, with the exception of 3 -> 4, which is initiated by the cashless device on a valid card read.