Apple Attachment Unit Interface

Apple Attachment Unit Interface

Apple Attachment Unit Interface (AAUI) is a mechanical re-design by Apple of the standard Attachment Unit Interface (AUI) used to connect Ethernet transceivers to computer equipment. AUI was popular in the era before the dominance of 10BASE-T networking that started in the early 1990s; AAUI was an attempt to make the connector much smaller and more user friendly.

AUI used a full-sized 15-pin D connector (model DA-15) that used a sliding clip for mechanical connections in place of thumbscrews. AAUI replaced these with a small 14-position, 0.050-inch-spaced ribbon contact connector. The connector was locked into position using two clips on the side of the connector which automatically clicked on when plugged in, and could be removed simply by squeezing small flanges on the side of the connector housing. The connector may also have been changed to avoid confusion with the monitor port on early Macintoshes, which also used a 15-pin D connector.

AAUI signals have the same description, function, and electrical requirements as the Attachment Unit Interface (AUI) signals of the same name, as detailed in IEEE 802.3-1990 CSMA/CD Standard, section 7, with the exception that most hosts provide only 5 volt power rather than the 12 volts required for most AUI transceivers. An adapter containing a power supply to provide the required 12 volts was available from Apple to permit connection of standard AUI transceivers to an AAUI port - this facilitated direct connection to 10BASE-F (fibre optic) and 10BASE5 (ThickNet) Ethernet networks, for which AAUI transceivers were not available.

AAUI was part of a system of ethernet peripherals that tried to make connecting to Ethernet much easier. At the time, Ethernet systems usually were 10BASE2, also known as thinnet. Apple's system was called FriendlyNet. A FriendlyNet 10BASE2 system did not use BNC T-connectors or separate 50 Ω terminators. The AAUI transceiver had two BNC connectors instead of one and a cable was attached to each side. The transceiver would automatically terminate the network if a cable was not attached to one of the sides. Additionally, Apple cables would terminate the network if no device was attached to them. Thus the number of mistakes that could be made hooking up a thinnet network was reduced considerably. Since any of these mistakes would disable the network in an area this was a significant improvement. However, the FriendlyNet equipment was quite expensive. As 10BASE-T became ubiquitous it became difficult to justify the cost of an external transceiver and Apple abandoned the system and sold off the name.

Macintosh Quadra, Centris, PowerBook 500, Duo Dock II (for PowerBook Duo) and early Power Macintoshes had an AAUI port, which requires an external transceiver. Generally the transceivers cost a significant percentage of the cost of a low-cost Ethernet card on the PC. Later models included both an AAUI and RJ-45 port for directly connecting 10BASE-T; either could be used, but not both at the same time. AAUI connectors were also present on some Processor Direct Slot Ethernet adapter cards used in Macintosh LC and Performa machines. AAUI had disappeared by the late 1990s, when all new Apple machines included only 10BASE-T.

The pin-out is:

Pin Signal Name Signal Description
1 FN Pwr Power (+12 V @ 2.1 W or +5 V @ 1.9 W)
2 DI-A Data In circuit A
3 DI-B Data In circuit B
4 VCC Voltage Common
5 CI-A Control In circuit A
6 CI-B Control In circuit B
7 +5 V +5 volts (from host)
8 +5 V Secondary +5 volts (from host)
9 DO-A Data Out circuit A
10 DO-B Data Out circuit B
11 VCC Secondary Voltage Common
12 NC Reserved
13 NC Reserved
14 FN Pwr Secondary +12 V @ 2.1 W or +5 V @ 1.9 W
Shell Protective Gnd Protective Ground

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