Gilbarco Dispenser Twowire Protocol For Third Party Pump - Controllers New

The protocol operates on a Master-Slave architecture. The Third-Party Controller acts as the Master, and the Dispensers are Slaves.

The Gilbarco Two-Wire Protocol (often referred to as "Type A" or "Current Loop") is a legacy serial communication standard used to control fuel dispensers. For third-party pump controllers (non-Gilbarco POS), this protocol allows basic fuel authorization, grade selection, and transaction monitoring without requiring a full Gilbarco G-SITE or Passport controller.

This document outlines the specifications for new third-party controller integrations. The protocol operates on a Master-Slave architecture

Any third-party controller interacting with the dispenser must not bypass security checks.

The controller software must be programmed to interpret the specific timing and voltage levels associated with the Gilbarco Two-Wire standard. The controller software must be programmed to interpret

| Challenge | Description | Recommended Solution | | :--- | :--- | :--- | | Collision Detection | In multi-drop wiring, two pumps replying simultaneously can corrupt data. | Implement strict timing delays in the polling loop; verify Checksums on every received packet. | | Firmware Variations | Older pumps (V/R, Highline) vs. new pumps (Encore) may have slight firmware variances. | Design the software to auto-detect firmware versions or maintain a "Configuration Table" for specific pump models. | | Half-Duplex Limitations | The Two-Wire system cannot transmit and receive simultaneously. | Enforce a strict "Turnaround Delay" (e.g., 5ms) after sending a command before switching the UART to listen mode. | | Ground Loops | Electrical noise from pump motors interfering with data signals. | Hardware solution: Use Isolated Current Loop Converters. |

Historically, a third-party controller had to mimic Gilbarco’s "polling" (asking each dispenser 10x per second). The new converters handle this polling internally. Your controller simply sends a command string: this protocol allows basic fuel authorization

*04P12000L

Breakdown: Start (*), Address (04), Preset (P), 2000 (cents), Stop (L).

The converter then translates this into the two-wire current loop pulse train. Within 50ms, the Gilbarco dispenser activates the relay for that hose.