Understanding MDB Levels and How They Affect Vending Operations
The Multi-Drop Bus (MDB) protocol defines how vending machines and payment systems communicate. Understanding MDB levels helps you choose the setup that delivers smoother transactions, faster service, and a better customer experience.
General
Understanding MDB Levels
The MDB (Multi-Drop Bus) level determines how a vending machine manages payments and user interactions. Each level offers a different balance of control, flexibility, and speed.
💳 Level 1 — Pre-Pay Mode
Flow: Users must insert cash or tap a card before selecting a product. The machine pre-authorizes a set amount upfront.
User Experience: Slower and more rigid when payment comes first, similar to a gas pump pre-authorization.
Level 1 setups are often used in environments where pre-payment control is required or where offline operation is needed.
🛒 Level 2 — Semi-Flexible Mode
Flow: Adds features like multi-purchase options. The system may still pre-authorize but allows users to select multiple products before confirming payment.
User Experience: Smoother than Level 1 that offers more flexibility while maintaining transaction security.
Level 2 is ideal for machines offering bundled purchases or where users often buy more than one item per session.
⚡ Level 3 — Post-Pay Mode
Flow: The machine stays in an “always idle” state, letting users select items first and pay afterward.
User Experience: Fast and intuitive, users browse freely and then pay, much like a traditional retail checkout.
Level 3 provides the most seamless experience, reducing friction and supporting contactless or app-based payments.
Summary
| Level | Payment Timing | Experience | Flexibility |
| 1 | Before selection | Slower, secure | Low |
| 2 | Before checkout | Moderate | Medium |
| 3 | After selection | Fast, retail-like | High |
Tip: Choosing the right MDB level directly affects user convenience, transaction speed, and customer satisfaction. Level 3 offers the best experience for modern, contactless vending environments.
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