Chris G Demetriou <Chris_G_Demetriou@ux2.sp.cs.cmu.edu> writes:

> 
> > - A PS/2 mouse port is a serial port specially designed for mouse use;
> >   it isn't capable of variable speed transfer, and in some cases, is
> >   input-only.
> 
> [...]
> 
> I think you're right that it's fixed speed (like the keyboard port,
> no?), but i'm almost certain that it's not spec'd to be input-only.

Indeed, the protocol *requires* transmitting data in both directions.
You have to send it some bytes even to tell it to start sending data.

The `mouse' port is a second nearly identical channel on the keyboard
controller.  I've been meaning to try plugging a second keyboard into
it, actually.