There was a time when if you bought a USB mouse, in the box was also an adapter to allow it to be used with the older PS/2 interface. And if you were to go back a few more years into the past ...

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. As it turns out, there’s a wealth of ...