Abstract: A keyboard is provided, in which only alternate keys of each row of keys and only alternate keys of each column of keys are connected to switches; and in which a square array consisting of four adjacent keys is associated with each of a plurality of symbol fields. Each of the keys, with the exception of the terminal keys of the rows and columns, are associated with four symbol fields provided with respective symbols. The switches are connected to row conductors associated with respective rows of keys and to column conductors associated with respective columns of keys. In conjunction with such a keyboard, commercially available decoders can be used for decoding if interrogation input signals are delivered to consecutive input terminals and consecutive output terminals are tested for the presence of output signals.

Abstract: A key array in which, progressing from key to key, the switching functions are derived by an AND-operation from mechanical or electrical signals indicating the actuation of pairs of adjacent keys of a row of keys or indicating the actuation of at least two diagonally opposite keys of a square group of four keys arranged in a rectangular keyboard. The pairs of adjacent keys and the square groups of four keys, respectively, each are allocated to a single symbol and each are depressable simultaneously by the operator's fingertip in order to initiate the single respective switching function. Thereby, a large surface lying in one single plane and being divided by gaps between the respective keys of one pair of keys or one group of keys, is available for the symbol legend and for engagement by the fingertip.