Circuit for detecting keypad conditions in a microprocessor...

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

H - Electricity

04

M

379/20

H04M 1/50 (2006.01) H04M 1/26 (2006.01)

Patent

CA 1235239

CIRCUIT FOR DETECTING KEYPAD CONDITIONS IN A MICROPROCESSOR CONTROLLED TELEPHONE INSTRUMENT ABSTRACT OF THE DISCLOSURE 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 ab- solute 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 require- ments to the available ports of a specific micropro- cessor.

484094

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