GB1380282A - Keyboards - Google Patents

Abstract

1380282 Keyboards ILLINOIS TOOL WORKS Inc 17 May 1972 [19 May 1971] 23251/72 Heading G4H A keyboard has a matrix of actuable devices which are scanned cyclically to produce an output which is stored and compared with the output one scan cycle later to detect changes. A clock-driven counter 20 drives the column lines of a keyboard matrix 10 in turn, a common drive-return line 50 being provided for noisecancellation. As each column is driven, row sense lines are scanned in turn by a multiplexer 18 controlled by the counter 20. A magnetic core 26 is provided at each of these row-column intersections, and depression of a corresponding key moves two magnets to desaturate the core and produce coupling of a drive pulse to the sense line. A further sense line, threading no cores, provides a common mode signal from which the multiplexer output is subtracted at 54 prior to summing 57 with a feedback signal from the shift register output (see below) for noise reduction. The summer output is thresholded, 58, and stretched, 60, to provide a strobe pulse via a pulse generator, 67, and gate 68, the signal also entering a shift register 70 to provide a one-scan-cycle delay, the shift register output being used to inhibit the gate 68 via an inverter 76 to prevent repeated outputs. The counter 20 provides a coded output to accompany the strobe signal, the coded output being recoded if necessary for case shift or control mode in a translator 100. A parity bit is generated at 110. Key positions corresponding to functions are recognized by decoders 88 responsive to the. counter 20 to inhibit the strobe signal at gate 68 and set respective flip-flops 84 if enabled by the output of inverter 76.