Compatibility
Payment gets into a machine through its controller, and there are only four ways in. Say what the machine is and we will tell you which one it almost certainly is — and what that path can and cannot give you.
Nobody buying this knows their protocol, and they should not have to. What an operator knows is the machine: what it is, what it takes today, roughly how old it is. That is enough to name the path with useful confidence.
What it is not enough for is a promise. The connector on the controller board settles it, and that is a photograph, not a dropdown — so the answer below ends with the question worth sending us.
Every machine we have connected in thirty years arrived through one of these. They are listed in descending order of how much the machine can tell you afterwards.
The machine already has a bus for payment peripherals, and the terminal joins it as a cashless device — alongside the coin unit, not instead of it. The machine's own controller keeps running the machine; payment negotiates with it rather than replacing it.
What it does not give: Nothing meaningful — this is the richest path there is. What varies is how completely a given machine implements the standard, which is an integration detail rather than a limit.
Where a machine has no usable payment bus but does have a controller we can talk to, the terminal drives that board directly instead of joining a bus. It is more work per machine model and it gives back nearly everything MDB does.
What it does not give: It is model-specific: what we learn on one controller does not automatically carry to another manufacturer's board.
Machines that were never built as vending — car washes, chargers, lockers, laundry — are run by an industrial controller instead. It has no concept of a cashless device, so payment arrives as an input it already understands: registers and coils over Modbus.
What it does not give: What the PLC exposes is what you get: if a cycle state is not in a register, no amount of software puts it there.
The machine is waiting for one thing: the electrical signal a dropped coin makes. The terminal takes the payment and then closes a contact, and the machine starts — exactly as if a token had gone in.
What it does not give: There is no return path. The machine cannot tell the terminal that it ran out, jammed or delivered nothing — so stock levels and delivery confirmation are not available through this route, and a refund is a decision someone makes, not one the machine reports.
A picture of the controller board and its connectors turns the likelihood above into an answer. No obligation attached to asking.