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
The cashless device is basically a state machine with 5 states (7 for level 2 and 3 machines). These states are:
- Inactive
- Disabled
- Enabled
- Session Idle
- 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 | ||
| Vend | Vend Request | Vend Approved | Required | XX |
| Vend Denied | Required | XX | ||
| Vend Cancel | Vend Denied | Required | XX | |
| Vend Success | ACK | Required | XX | |
| Vend Failure | ACK | Required | XX | |
| Session Complete | End Session | Required | XX | |
| Cash Sale | ACK | Required | XX | |
| Reader | Reader Disable | ACK | Required | XX |
| Reader Enable | ACK | Required | XX | |
| Reader Cancel | Cancelled | Required | XX | |
| Expansion | Request ID | Peripheral ID | Required | XX |
| Diagnostics | Diagnostic Response | Required | XX |