26 pin Sun AUI connector at the computer.
Sun Microsystems used a 26-pin HD-26 mini-D-sub connector on the SPARCclassic, SPARCclassic X, and SPARCstation LX workstations as a proprietary extension of the standard IEEE 802.3 AUI (Attachment Unit Interface). The six core AUI signal pairs — Data Out, Data In, and Collision (Control In) with their complements — occupy pins 1–3 and 14–16, preserving electrical compatibility with standard 10 Mbit/s AUI transceivers via a breakout cable. The remaining pins carry Sun-specific signals including the CHI audio codec bus, MIDI input and output, Ethernet power, reset sense, and codec power control, effectively merging the Ethernet transceiver attachment interface and the SpeakerBox audio interface into a single rear-panel socket. The connector was introduced in the early 1990s and required a dedicated HD-26-to-DA-15 cable to attach a conventional thick-Ethernet transceiver.
| Pin | Name |
|---|---|
| 1 | Transmit - |
| 2 | Receive + |
| 3 | Collision - |
| 4 | AUI Power |
| 5 | N/C |
| 6 | N/C |
| 7 | N/C |
| 8 | N/C |
| 9 | N/C |
| 10 | N/C |
| 11 | N/C |
| 12 | N/C |
| 13 | N/C |
| 14 | Transmit + |
| 15 | Receive - |
| 16 | Collision + |
| 17 | Ground |
| 18 | N/C |
| 19 | N/C |
| 20 | N/C |
| 21 | N/C |
| 22 | N/C |
| 23 | Ground |
| 24 | Ground |
| 25 | N/C |
| 26 | Ground |
Signals
- Transmit +/− — Data Out differential pair (AUI DO-A/DO-B); Manchester-encoded 10 Mbit/s transmit data from the DTE to the MAU transceiver.
- Receive +/− — Data In differential pair (AUI DI-A/DI-B); received data from the MAU to the DTE.
- Collision +/− — Collision presence (Control In) differential pair (AUI CI-A/CI-B); signals a collision detected on the medium by the transceiver.
- AUI Power — Supply voltage to the AUI transceiver (Ethernet power rail).
- Ground — Signal and chassis ground returns (pins 17, 23, 24, and 26).
- Pins 5–13, 18–22, and 25 — Functions not represented in this pin table; the SPARCclassic service manual documents these positions as carrying CHI audio codec bus signals (EMCTL, CHIDX, CHI_CLK, CODFS, CHIDR, CHIDFS, CODCK), MIDI I/O (MIDI_IN, MIDI_OUT, MIDI_IN_L), codec power-down control (Codec_PWR_DN_L), reset sense (RESET_SENSE_L), and additional Vcc lines.
Notes
- The HD-26 connector is Sun’s proprietary 26-pin variant; it is not a standard 15-pin DA-15 AUI port and requires a dedicated HD-26-to-DA-15 adapter cable to connect to a conventional IEEE 802.3 thick-Ethernet transceiver.
- The six AUI signal pairs on pins 1–3 and 14–16 are electrically compatible with the standard AUI defined in IEEE 802.3, Section 7; signal impedance and Manchester-encoding requirements are identical.
- AUI supports a maximum cable length of 50 metres (164 ft) between the DTE and the MAU, with 77-ohm termination required at each end.
- The same HD-26 connector type was used on the SPARCstation 10 and SPARCstation 20 for the same combined Ethernet/audio purpose.