Macintosh: Do Not Split ADB Signal

Some Macintosh computers, like the Macintosh IIsi, have only one ADB port in the back. Can I make up my own ADB "T" plug or "Y" cable, so that two ADB sockets would be provided from the one port? Will the two ADB devices interfere with each other?

Another way to phrase the question: on a Macintosh with two ADB ports on the back, does each port come off a different and separate part of an interface chip, or are the two connections "common", so that pin 1 on connector 1 is connected to pin 1 on connector 2?

We do not recommend splitting the ADB signal, because it could cause difficulties with signal integrity. The signal is not very strong, and if split would be even weaker.

On a Macintosh with two ADB ports, both ports both go to the same ADB controller chip, but are physically separated to deliver the full signal down the bus.

Published Date: Feb 18, 2012