A computing device includes a system control processor, a built-in keyboard having a plurality of keys, a connector which facilitates connection of an external keyboard or keypad to the device, an electronic switch which is controlled by the internal keyboard processor and can electrically couple the...http://www.google.co.uk/patents/US5136694?utm_source=gb-gplus-sharePatent US5136694 - Method and apparatus facilitating communication between two keyboards and a single processor
