ADB Traffic Sniffer for Classic Macintosh and Apple IIGS Computers
Big Mess o’ Wires is building an ADB traffic sniffer and so far the progress looks promising. There are some discrepancies between the IIGS and vintage Mac, and even some errant key presses, but the host computer’s traffic does register clearly:
The image above shows ADB traffic from a Macintosh SE, at the moment when I began to move the mouse. At first the Mac was repeatedly polling the keyboard (device address 2) by asking it to “talk” register 0, which is the primary data register for an ADB device. The keyboard didn’t have any keypresses to report, so it didn’t reply. At the end of one of these transactions, the mouse pulled the ADB data line low in order to request service for itself – this is the SRQ flag shown in the traffic log.