I am quite aware you can get ready made off the shelf adaptors to connect old ps/2 keyboards to USB. But I am curious as how would one do it themselves? I have tried just rewiring an old keyboard to a USB cable as they both have 5V and ground and 2 data connections. Though USB has a differential DATA +- and ps/2 has a data and clock wire.

So after trying a basic rewiring it didn't work so there has to be some conversion going on but what? The puzzling thing is going from USB to PS/2 works but going the other way doesn't work? Why?

Can anyone point to the basic differences, initial googling took me to useless forums and dead ends.

Thanks