PS/2 keyboards are getting rarer, and I knew I had successfully used one of the USB to PS/2 adapters before, but for some reason it no longer worked. So, out came the oscilloscope again.

What I found was that the keyboard (or probably it was the adapter) was continually sending the 0xaa value every 600 ms. That value, 0xaa, is the 'Basic Assurance Test' (BAT), meaning that the keyboard passed the power-on self-test. But why was it sending it repeatedly, and not sending any key codes?

I hazarded a guess that it want some interaction from the host, so I sent the 'set LEDs' code upon reception of the BAT. Doing so seemed to take the adapter out of whatever state it was in, and restored relaying of keycodes from the USB keyboard.

While I had my probe wires soldered to the board, I tried a USB wireless keyboard through the adapter. This did not work. Unlike as with the wired USB keyboard, in this case the adapter simply remained silent.

So, I've checked all that in, and you should now be OK to use one of those adapters with the emulator, with a more modern USB (wired) keyboard if you don't have a native PS/2 one on-hand.