DIGITAL ETHERNET UNIBUS Network Adapter Technical Manual

This document is a Technical Manual for the DIGITAL ETHERNET UNIBUS Network Adapter (DEUNA), published by Digital Equipment Corporation in December 1982.

The DEUNA is a data communications controller designed to interface VAX-11 and PDP-11 family computers to an Ethernet local area network. It fully complies with the Ethernet specification, operating at a 10 Megabits per second (Mbps) data rate over shielded coaxial cable using a branching bus topology, supporting up to 1024 addressable devices.

Key aspects of the DEUNA and its operation include:

• Ethernet Protocol Implementation: It handles both physical and data link layer functions, including Carrier Sense, Multiple Access with Collision Detect (CSMA/CD) for channel access. This involves carrier sensing, collision detection, automatic retransmission with a controlled randomization process (backoff), and management of interpacket delays.
• Data Handling: The DEUNA performs data encapsulation and decapsulation, Manchester encoding and decoding, and calculates/verifies a 32-bit Cyclic Redundancy Check (CRC) for error detection.
• Address Management: It supports filtering based on physical, multicast, and broadcast addresses, with hardware comparators for efficient address detection.
• Internal Architecture: The DEUNA is microprocessor-based, utilizing a T11 microprocessor and its microcode to manage data link functions, channel access, and network maintenance, aiming for maximum data throughput with minimum host processor intervention. It incorporates a 32 KB (16 KW) buffer for continuous datagram reception and transmission.
• System Interface: It connects to the host system via the UNIBUS, functioning as both a bus master (for Direct Memory Access, DMA, to transfer data to/from host memory) and a bus slave (for host access to its control and status registers).
• Physical Components: It consists of two hex-height modules (a Port Module and a Link Module), an interconnect panel, and cables, connecting to the Ethernet coaxial cable via a DIGITAL H4000 transceiver.
• Diagnostics and Maintenance: The device features extensive diagnostic capabilities, including internal ROM-based microdiagnostics for self-testing, Time Domain Reflectometry (TDR) for cable fault detection and localization, and comprehensive loopback testing options.

In essence, the DEUNA is a dedicated hardware controller designed to efficiently offload much of the Ethernet communication processing from the host computer, providing robust and high-speed network connectivity.