You know, those little green adaptors that you sometimes get with USB mice, enabling them to plug into a PS2 port - do they have any/much in the way of circuitry inside, or is the gestalt of [electronics inside the mouse + software drivers] sufficient to make it a simple case of connecting things to the right place?
I’ve taken one apart. There’s nothing in there, it’s just two connectors wired together. The circuit inside the mouse must be smart enough to figure out whether it’s connected to a USB or PS2 port and act accordingly.
Exactly as scr4 says.
For what it’s worth the wiring goes like this:
usb - ps/2
GND - 5 GND
RxD - 2 RxD
TxD - 3 TxD
+5V - 7 RTS