Circuit for detecting keypad conditions in a microprocessor cont

Details Circuit for detecting keypad conditions in a microprocessor cont Circuit for detecting keypad conditions in a microprocessor cont

1984-11-13

1986-07-01

Dwyer, James L.

179 84R, 179 81R, 179 90K, H04M 100

Patent

active

045981744

ABSTRACT:
A technique for evaluating keypad conditions while utilizing only a minimum number of ports in a microprocessor involved in control of a telephone instrument. Because of the limited number of ports available and necessity to also evaluate conditions of mode selecting strap switches, the utilization of a reduced number of ports is highly desirable in such an enviroment. Such a reduction becomes an absolute necessity particularly in dealing in those enviroments that include random access memories, read only memories, pulse dialers, integrated circuits and liquid crystal displays. A combination of diode gating, resistive decoupling and time multiplexing techniques are used to match the input/output requirements to the available ports of a specific microprocessor.

REFERENCES:
patent: 4298775 (1981-11-01), Buck et al.
patent: 4453040 (1984-06-01), Wolf et al.
patent: 4463221 (1984-07-01), Soulliard et al.
patent: 4475013 (1984-10-01), Lee et al.
patent: 4503291 (1985-03-01), Von Holten et al.
patent: 4513175 (1985-04-01), Smith

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