The serves as the primary communication link between millions of fuel dispensers and Point of Sale ( POS ) forecourt controllers worldwide . Originally developed as a proprietary data standard by Gilbarco Veeder-Root , this protocol has become an essential integration requirement for third-party automation systems. Independent developers of forecourt controllers, payment kiosks, and fleet management software must thoroughly understand both the physical and logical layers of this communication structure to achieve seamless hardware interoperability. The Physical Layer: Active Current Loop Electronics
Accumulated units (Gallons or Liters) measured via the pulser. Grade Selected: The active fueling product. 5. Developing Third-Party Hardware Controllers
The controller acts as the master, initiating all communication. Every unit in the loop receives the data, but only the addressed dispenser responds. Interfacing with Third-Party Controllers
5787 bps (historically) or 4800 bps / 9600 bps (modern configurations). Data Bits: 8 bits. Parity: Even parity. Stop Bits: 1 stop bit. 2. Network Topology and Addressing The serves as the primary communication link between
If you are planning to a third-party controller that claims two-wire support, ask the vendor:
The Master continuously sends a status poll to every active pump address. The dispenser responds with its exact operational state: The pump is ready, and the nozzle is hung up.
The true power of the Two-Wire Protocol lies in its ability to liberate station owners from single-vendor lock-in. The protocol is explicitly named for use by "Third-Party Pump Controllers," and a thriving ecosystem of hardware and software has grown around it. dispenser preparing to pump.
Adopting the Two-Wire Protocol for third-party control offers tangible business and operational benefits:
The Gilbarco Two-Wire protocol is a proprietary, standard used to link fuel dispensers with point-of-sale (POS) systems or third-party pump controllers . It operates as a master-slave system where the controller (master) initiates all communication, and individual dispensers (slaves) respond only when addressed. 1. Technical Specifications
The Gilbarco dispenser two-wire protocol is a master-slave protocol that uses a two-wire serial communication link between the pump controller (master) and the dispenser (slave). The protocol is based on a simple, asynchronous serial communication standard, with a single master device (pump controller) and multiple slave devices (dispensers). asynchronous serial communication standard
| Pitfall | Consequence | |---------|--------------| | Using RS-232 levels directly | Destroy dispenser’s optocoupler | | Ignoring parity bit | Random transaction failures | | Polling faster than 200 ms | Dispenser lockup (floods buffer) | | No timeout handling | System hangs if dispenser offline | | Assuming same polarity on all models | Some older Gilbarco models swap loop + and - |
For a new third-party controller to successfully operate Gilbarco dispensers via the Two-Wire Protocol, the following integration points must be addressed:
The open-circuit voltage of the loop is usually capped between 24V DC and 35V DC .
Historically 5787 baud (a unique standard specific to Gilbarco). Modern dispensers and newer third-party controllers frequently utilize 9600 baud . Data Bits: 8 bits Parity: Even Stop Bits: 1 bit 3. Protocol Framing and Architecture
Controller approved the sale, dispenser preparing to pump.