Keypad logic interface circuit
AssigneeBell Telephone Laboratories, Incorporated
InventorJoseph J. Nahas
Life of this patent
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Abstract
A keypad logic interface circuit (200) provides a switch closure output signal representative of a selected one of a plurality of digits on a crosspoint contact array keypad (100). The selected one of the plurality of digits provides the switch closure signal by diverting a source current (225) from a first to a second direction. The circuit encodes each one of four column outputs from the keypad into a two-bit code. An output signal from two or more columns at the same time causes the circuit to produce an inhibit output signal reflecting a multiple button-push condition. The circuit also encodes each of four row outputs from the keypad into a two-bit code and produces an inhibit output signal when multiple row output signals are received.
Claims5
A keypad interface circuit (200) for providing an output switch closure signal representative of a selected one of a plurality of digits on a keypad (100), the keypad interface circuit comprising:
- a keypad detector circuit that includes a plurality of identical low group sections and a plurality of identical high group sections for detecting a switch closure on the keypad;
- each low group section providing a signal representative of the switch closure for a particular row of digits and each high group section providing a signal representative of the switch closure for a particular column of digits, characterized in that:
- the signal from each low and high group section in combination providing the switch closure signal;
- and
- the switch closure signal being determined by diverting a current provided by a current source from a first to a second direction.
Dependencies are inferred from the claim text.