It will allow you to connect either a PS/2 keyboard or a USB keyboard in fallback mode to the Expert using an ATMega328P and a bespoke DIN-13 to DB-13 cable.

Connect the Microsoft keyboard's USB cable to an available USB port on your Mac computer. If it is a PS/2 keyboard, connect the keyboard cable to a PS/2 adapter and then connect the adapter to ...

Some of the Logitech ones won't work with Microsoft mice, and vice versa, even.<BR><BR>They do make generic PS/2-USB adapters (Belkin has one), but you want the other way around, and that just ...

The USB port on [Deater’s] PCB, by the way, allows you to connect some USB keyboards that fall back to PS/2 mode with an adapter. You can’t just plug any USB keyboard into it.