PS/2 Interface (was: Wang 300 Calc]

--------------Original Message: Date: Fri, 14 Sep 2007 21:09:17 +0100 (BST) From: ard at p850ug1.demon.co.uk (Tony Duell) Subject: Re: Wang 300 Calc IIRC, the PS/2 mouse interface and PS/2 keyboard interface are very similar. Both are TTL level interfaces with clock and data lines, both have 4 signals on the connector (+5V, ground, clock, data), and the data transfer protocol is much the same. IIRC, the pin assignemts of the 2 interfaces is the same too, and it's possible to make a device where you can plug the mouse and keyboard into either connector, and detect what sort of device is plugged into a given socket. The fact that most PCs didn't let you do that is not the fault of the interface. So why not use the same connector for the 2 interfaces? -tony -----------------Reply: Why not indeed; old Compaq laptops have a single connector which will accept either a mouse or an external keyboard (an external key_pad_ used a submini earphone-type connector). IBM allowed for both together; a mouse or external keypad connected directly to the single connector while an external keyboard required a Y adapter which routed the keyboard clock & data signals to the two unused pins. And then there are the dual-mode mice which put RS-232 on the unused pins and came with an adapter so they could be used either way... Laptops were probably also a reason for reducing the size of the connector. "Criminally stupid"? I suppose you'd also want incompatible connectors for the right & left channels of your stereo? ;-)