Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1980-06-09
1982-06-15
Groody, James J.
Communications: electrical
Audible indication
Percussion-type sound producer
364707, G06F 302
Patent
active
043353746
ABSTRACT:
A key discrimination circuit for determining which key among a plurality of keys disposed in a matrix is actuated and which generates less electrical noise than prior art key discrimination circuits. In prior art key discrimination circuits, one set of lines forming the key matrix are continuously scanned while a plurality of AND gates are cyclically enabled thereby determining the actuated key or keys according to the time an output signal is generated. Because the continuously scanned set of lines are long and have "1" and "0" level signals periodically appearing thereon, they tend to generate electrical noise. In the key discrimination circuit of the present invention, initially all the lines in one set of lines have a "1" level applied thereto. A separate circuit determines when any key is actuated. Only when it is determined that at least one key is actuated is the key matrix scanned to determine the key or keys actuated. Therefore, the set of lines are intermittently scanned only when it is necessary to determine which key is actuated, thereby reducing the electrical noise generation.
REFERENCES:
patent: 3818441 (1974-06-01), Nomiya et al.
patent: 3900845 (1975-08-01), Tsuiki et al.
patent: 4138916 (1979-02-01), Kitagawa
patent: 4138917 (1979-02-01), Sakashita et al.
patent: 4148017 (1979-04-01), Tomisawa
Groody James J.
Matsushita Electric - Industrial Co., Ltd.
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