Abstract: There is disclosed herein a data entry device designed for general use, and whose functional configuration may be readily changed to meet the specific needs of a number of different customers, each requiring a special assortment of operational features. The device (10) includes a housing (12) having a keyboard (14) including function control and data entry portions (18 and 20). In one embodiment, a plurality of different overlays (22) may be received over the function control portion of the keyboard. Each overlay carries an array of key labels (26), and is pliant enough to permit an underlying key to be actuated by depressing an appropriate key label. Tabs (30, 32, 34) projecting from the frame (24) carrying the overlay actuate switches (132, 134, 136) in the device to identify which overlay is carried by that frame. Other means of identifying the overlays to the data entry device are also shown. A different, permanent set of keys is provided for data entry in this embodiment.

Abstract: A mechanical interlock for a hand held data processing device which prevents removal of an alternate electric power source when a separate power source is disengaged from the device and the electronic circuitry powered by it.The technical problem addressed by this invention is that of preventing adverse effect on electronic circuitry, such as loss of data stored in memory, due to removal of all electric power therefrom by assuring an uninterrupted source of electric power.