26 pin Sun AUI connector
The Sun AUI connector is a proprietary 26-pin high-density D-Sub interface found on SPARC workstations and SPARCengine motherboards from the early 1990s onwards. Unlike the standard IEEE 802.3 Attachment Unit Interface, which uses a 15-pin DA-15 shell, Sun’s implementation uses a smaller 26-pin housing that carries the same differential Ethernet signal pairs (Transmit±, Receive±, Collision±) alongside additional functions. On SPARCclassic and SPARCstation LX systems, the same 26-pin connector also multiplexes a CHI audio codec bus, MIDI input and output, codec power-down, and reset-sense lines, making it a multi-function I/O port rather than a pure Ethernet AUI. The SPARCengine 5 used a similar 26-pin variant carrying only the Ethernet differential pairs without audio or MIDI multiplexing.
| Pin | Signal | Description |
|---|---|---|
| 1 | AUI_DO_L | |
| 2 | AUI_DI | |
| 3 | AUI_CI_L | |
| 4 | ENET_PWR | |
| 5 | EMCTL | |
| 6 | CHIDX | |
| 7 | CHI_CLK | |
| 8 | CODFS | |
| 9 | N/C | |
| 10 | Vcc | |
| 11 | Vcc | |
| 12 | Codec_PWR_DN_L | |
| 13 | MIDI_IN | |
| 14 | AUI_DO | |
| 15 | AUI_DI_L | |
| 16 | AUI_CI | |
| 17 | GND | |
| 18 | RESET_SENSE_L | |
| 19 | CHIDR | |
| 20 | CHIDFS | |
| 21 | CODCK | |
| 22 | N/C | |
| 23 | GND | |
| 24 | GND | |
| 25 | MIDI_OUT | |
| 26 | MIDI_IN_L |
Signals
- AUI_DO_L / AUI_DO — Differential Data-Out (Transmit) pair (pins 1 and 14); carries outgoing Ethernet data from the station to the external transceiver, conforming to IEEE 802.3 AUI signalling levels.
- AUI_DI / AUI_DI_L — Differential Data-In (Receive) pair (pins 2 and 15); carries incoming Ethernet data from the transceiver to the station.
- AUI_CI_L / AUI_CI — Differential Collision-Indicate pair (pins 3 and 16); signals a collision on the Ethernet medium, as defined by IEEE 802.3 AUI.
- ENET_PWR — Ethernet transceiver power supply (pin 4); provides bias voltage to the attached external AUI transceiver or MAU.
- EMCTL — Ethernet medium control (pin 5); function is platform-specific; not part of the standard IEEE 802.3 AUI signal set.
- CHIDX — CHI codec data transmit line (pin 6); part of the Serial CHI (Codec/Host Interface) bus used to communicate with the on-board audio codec.
- CHI_CLK — CHI bus clock (pin 7); clocks the CHI serial data transfers between the host and the audio codec.
- CODFS — Codec frame-sync signal (pin 8); provides the sample-rate frame synchronisation pulse for the CHI audio codec bus.
- N/C — No connection (pins 9 and 22); reserved, leave unconnected.
- Vcc — +5 V logic supply (pins 10 and 11).
- Codec_PWR_DN_L — Codec power-down, active-low (pin 12); asserted low to place the audio codec into a low-power state.
- MIDI_IN — MIDI data input, non-inverted (pin 13).
- RESET_SENSE_L — System reset sense, active-low (pin 18); allows the connector to signal or detect a system reset event.
- CHIDR — CHI codec data receive line (pin 19); receives serial audio data from the codec to the host.
- CHIDFS — CHI data frame-sync for the receive path (pin 20); provides frame-sync for the incoming CHI audio data stream.
- CODCK — Codec master clock (pin 21); supplies the master clock to the audio codec.
- GND — Ground (pins 17, 23, and 24).
- MIDI_OUT — MIDI data output (pin 25).
- MIDI_IN_L — MIDI data input, inverted (pin 26); forms the complementary signal to MIDI_IN for differential MIDI reception.
Notes
- This connector uses a 26-pin high-density D-Sub shell (female at the motherboard, male at the cable). It is physically incompatible with the standard IEEE 802.3 DA-15 AUI connector despite carrying the same core Ethernet differential pairs.
- The AUI differential pairs (DO±, DI±, CI±) follow IEEE 802.3 AUI electrical levels; the remaining pins carry TTL-level signals specific to Sun’s integrated audio and MIDI subsystem.
- On the SPARCclassic and SPARCstation LX, the connector serves as a combined Ethernet AUI, CHI audio codec, and MIDI port. On the SPARCengine 5, only the Ethernet differential pairs and power/ground pins are active; all audio and MIDI pins are unpopulated (N/C).
- Do not connect standard IEEE 802.3 AUI transceivers directly without confirming which variant of the 26-pin connector is fitted; the SPARCclassic/LX multi-function variant routes non-AUI signals on pins that a standard DA-15 adaptor would not expose, but accidental drive of those pins from an adaptor should still be avoided.
- All logic signals operate at TTL-compatible +5 V levels.
References
- SPARCclassic / SPARCclassic X / SPARCstation LX Service Manual, Part No. 801-2176-13 — Sun Microsystems, Inc., Revision A, November 1993; Appendix B documents the 26-pin AUI multi-function connector and SBus slot pinouts on production SPARC workstations.