Al dumped some NuBus cards as a Christmas gift. Least I can do is have one running before the end of the day.

This is the BootBug card, which installs a low-level debugger very early in the Mac's boot process (specifically, before other slot cards are initialized if you put it in the right slot), and is intended for debugging the firmware on other NuBus cards. I/O is through a PC standard 16C450 connected to a terminal at 9600 8/N/1.

[Linked Image from rbelmont.mameworld.info]