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.

Device Level

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.

States

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.

If the cashless device receives a command it cannot act upon in its current state, or receives an unexpected command whilst in an uninterruptable state it must ACK(nowledge) the command, then on the next POLL from the VMC, issue a COMMAND OUT OF SEQUENCE response.

The VMC will then respond with a RESET command, putting the reader back to state 1.

Uninterruptable States

During certain command sequences, the VMC should not issue any additional commands to the cashless device. These are the Uninteruptable States. If the VMC does issue any additonal commands during one of thes states, the reader should responds with COMMAND OUT OF SEQUENCE, as noted above.

These sequences for a level 1 device are:

VMC Command	Cashless Device Response	Result
SETUP/CONFIGURATlON DATA	READER CONFIGURATION DATA
EXPANSION/REQUEST ID	PERIPHERAL ID
READER CANCEL	CANCELLED
VEND REQUEST... VEND CANCEL	VEND DENIED
VEND REQUEST	VEND DENIED
VEND REQUEST	VEND APPROVED	VEND SUCCESS
VEND REQUEST	VEND APPROVED	VEND FAILURE
SESSION COMPLETE	END SESSION

The highlighted rows are all possible sequences in the vend state (state 5), so this state is completely uninterruptable.

Commands

Where a response is ACK, this can also be NAK (Not Acknowledged).

Command	Sub-command / Data	Response	Req?	Spec Page Num
Reset	(none)	ACK	Required	XX
Setup	Config Data	Reader Config Data	Required	XX
	Max/Min Prices	ACK	Required	XX
Poll	(none)	Just Reset	Required	XX
		Reader Config Data	Required	XX
		Display Request	Required	XX
		Begin Session	Required	XX
		Session Cancel Request	Required	XX
		Vend Approved	Required	XX
		Vend Denied	Required	XX
		End Session	Required	XX
		Cancelled	Required	XX
		Peripheral ID	Required	XX
		Malfunction / Error	Required	XX
		Command Out of Sequence	Required	XX
		Diagnostic Response	Required	XX