but i cannot find schematics for usb>ps/2 adaptor.
There is no such thing like an USB->PS/2 adapter. USB and PS/2 protocols are totally different. Either you use a mouse which supports both USB and PS/2, then it comes with the needed adapter. Or you use a mouse which supports USB only, then it cannot be used on a PS/2 bus, no matter if you plug it into an adapter or not.
However, I don't know of any USB mouse which comes without a PS/2 adapter.
Bye,
Thomas