Cookies and Capacitors

ADB hardware

Mon, Apr 30, 2012 at 4:44PM

I’m trying too hard to implement everything in software. What this ADB project needs is some good ‘ol fashioned hardware, to take some of the load off the tiny little AVR in the Arduino.

For instance, instead of switching a single pin between an input and output, why not just have two pins? And instead of writing the output pin low-then-high, why not just pull it high in hardware and send it low? That will save CPU instructions, too.

Looking on page 293 of the Apple Guide to Macintosh Family Hardware one can see the circuit for the Macintosh SE’s ADB transceiver. What I’ve done in this image is simplified it a bit. This is the schematic I’m using to connect peripherals to the Arduino, now.