Attachment Unit Interface

The AUI can operate in both normal mode and monitor mode. In normal mode, it functions as a direct connection between the DTE and the network medium. Monitor mode, an optional feature, isolates the MAU's transmitter from the medium while allowing the DTE to observe network activity. This mode is useful for diagnostic and monitoring purposes without impacting the physical medium. == Signaling and control ==

The AUI uses Manchester encoding for data transmission, which ensures clock synchronization without requiring a separate timing signal. The data and control circuits operate independently and are self-clocked. Control signals coordinate communication between the DTE and MAU, enabling error signaling, MAU isolation, and medium access requests. == Connector and signals ==

An AUI connector is a DA-15 (D-subminiature) type, where the DTE side has a female connector and the MAU side has a male connector. The connector often uses a sliding clip instead of the typical thumbscrews found on D-connectors, allowing the DTE and MAU to be directly attached, even when their size or shape would not accommodate thumbscrews. However, the clip mechanism is sometimes considered awkward or unreliable. In the case of incompatible fittings, the jackposts or sliding clip can be unscrewed and replaced, or adapter dongles and cables can be used. Electrically, the AUI's differential signals are designed for use with a 78 Ω cable and can transmit data between DTE and MAU at 10 Mbps over the standard's specified 50-meter length. AUI drivers and receivers are required to tolerate wiring faults without permanent impairment of the pair. Signal jitter is controlled to within 1.5 nanoseconds across the interface. == Pinout table ==

The DA-15 pinout is specified by the IEEE 802.3 standard and describes four differential pairs: == References ==