> For the complete documentation index, see [llms.txt](https://help.security.gallagher.com/knowledge-hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.security.gallagher.com/knowledge-hub/products/integrations/third-party-readers/wiegand/t-series-wiegand-troubleshooting-intro.md). # Wiegand overview Understand Gallagher Wiegand connectivity, protocol behavior, pull-up resistors, and device wiring. #### What hardware provides Wiegand connectivity to Command Centre? Wiegand connectivity to Gallagher Command Centre can be achieved via the following hardware: * 3000 Controller (legacy product) * Controller with a 4R or 8R plug-in module * A GBUS URI (Standard or Wiegand) * An 8 In 2 Out Door Module Wiegand Variant *** #### How does the Wiegand protocol work, and when are pull-up resistors needed? Wiegand is an open-collector protocol. The D0 and D1 lines are pulled high and the Wiegand device pulls them low to send data. **Voltage reference:** The voltage reference for Wiegand is typically 5V. Check the Wiegand device's specifications for exact voltage requirements. **Voltage swing / deviation:** Wiegand signals require a sufficient voltage swing to be read reliably. Noise or impedance issues on long cable runs can cause inconsistent reads. *** ### Pull-up resistors *How do I know if pull-up resistors are required?* If you are getting inconsistent data from the Wiegand device, pull-up or pull-down resistors on the D0 and D1 lines may be required. *How do I add pull-up resistors?* Add pull-up resistors between the D0/D1 lines and the supply voltage rail. Consult the Wiegand device documentation for recommended resistor values. Gallagher Technical Support can advise on specific configurations. ![Pull-up resistors on the D0 and D1 lines](https://328339335-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6bM8WhlBE9BYizPWJaPN%2Fuploads%2Fgit-blob-508415e708611d83e164543919adb0f69cae26ff%2FSECHUB-TSERIES-WIEGAND-01-pull-up-resistors.jpg?alt=media) *** #### How are a Wiegand device and a Gallagher device connected? Standard connections: * **D0 and D1** convey the card data. * **R out 1** pulls down the LED line to indicate an Access Granted event on the Wiegand device. * **R out 2** pulls down the Buzzer line to indicate an Access Denied event. > ⚠️ **Ground is common between the Gallagher and Wiegand hardware.** Power can be supplied externally, but the ground link between the two devices **must** be present. **After a valid credential is processed:** * R out 1 (LED) pulses on for door access time (default: 5 seconds). * R out 2 (Buzzer) will pulse once. **After an invalid credential is processed:** * R out 1 (LED) will do nothing. * R out 2 (Buzzer) will trigger on for the door access time (default: 5 seconds). --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://help.security.gallagher.com/knowledge-hub/products/integrations/third-party-readers/wiegand/t-series-wiegand-troubleshooting-intro.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.