Membrane computer keyboard and method

In a computer keyboard having an on-board microprocessor and ROM, an output port through which scan codes are directed to a computer CPU over a cable, wherein the cable is connected at its keyboard end to the output port of the keyboard by a keyboard connector plug and at its CPU end to the CPU keyboard input port by a CPU connector plug compatible with a particular CPU and the keyboard is of the type having a plurality of touch activated switches under a membrane onto which one of a plurality of different key layout overlays can be installed and wherein the microprocessor generates one of several possible internal signals in response to activation of a touch activated switch, the improvement comprising:

• a plurality of overlay mapping data tables stored in the on-board ROM wherein each overlay mapping data table has a plurality of levels and is associated with a particular key layout overlay;
• an overlay identification code on each key layout overlay,
• an overlay identification code detector on the keyboard responsive to a key layout overlay being installed onto the keyboard to detect said overlay identification code on the installed key layout overlay and generate a signal representative of such detected code;
• an overlay mapping data table selector in the microprocessor responsive to the signal generated by said overlay identification code detector to select a particular overlay mapping data table for use with the installed key mapping overlay;
• a CPU code on the keyboard connector plug identifying the particular CPU with which the CPU connector plug on the same cable is compatible;
• a CPU code detector on the keyboard for detecting said CPU code on a keyboard connector plug plugged into the keyboard and generating a CPU identifying signal;
• and
• an overlay mapping data table level selector in the microprocessor responsive to the signal generated by said CPU code detector to select a particular overlay mapping data table level for use with the CPU connected to the keyboard by the cable.