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Keyboard and Mouse: Easy as ADB

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Easy as ADB

The other bus. Most people are at least vaguely aware that there's a "bus" in the computer - usually they're thinking of the SCSI bus, the wires along which SCSI information travels. But there's another very important Mac bus; the Apple Desktop Bus, or ADB, that's used for basic input devices: the keyboard and the mouse, mouse substitutes like trackballs and trackpads, and even some scanners.

ADB chains. You can create a chain of ADB devices - a keyboard, a trackball, and a mouse, for instance. But since the mouse presents a dead end, it always has to be the last device. There are T- and Y-connectors available that let you branch two items (a mouse and a trackball, for instance) from a single ADB connector. And many devices, especially trackballs, come with "pass-through" connectors so you can plug in the new device and then the mouse.

There's a theoretical limit of sixteen ADB devices for the Mac, since there are sixteen different "addresses" that can be assigned internally to ADB devices to keep track of them. But you can really use only three or four in a chain (which, face it, ought to be plenty) because with more than that, the signal from the last device is too weak to reach the Mac. That's probably because the other ADB chain limitation kicks in: The total length of the chain shouldn't exceed five meters (about sixteen feet).

Live ADB unplugging. Although it's generally believed that plugging or unplugging an ADB connector while the Mac is turned on is a dangerous thing, it was a problem only on some early Mac models.

There was nothing inherently dangerous about the ADB on these machines, but the design of the logic board was such that a minor flexion of the board could occur if the ADB plug was inserted or removed a little too vigorously - resulting in a short from the ADB power line to the metal shielding on the inside of the case. Zap! And goodbye to the ADB fuse! Later Macs have thermal, self-resetting fuses which prevent this problem.

But you are left with this minor annoyance: If you have to connect your mouse after the computer's on, it's going to move the cursor very slowly, and using the Mouse control panel to reset the tracking speed isn't going to help much. You need to restart the Mac to get the mouse to behave correctly. - SZA/DR

The Plus's minus. The Mac Plus does not use the ADB standard for its keyboard or mouse, so you can't buy a new keyboard or mouse for it.

Getting along. If your keyboard wire is too short, get a different one. Computer supply catalogs and Web sites offer six-foot ADB cords in coiled and uncoiled varieties. My keyboard cable is attached to the back of the Mac CPU, then snakes around the back of a corner desk and under it, into the slide-out keyboard drawer. Try that with the standard cable!

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