Telephonic communications – Supervisory or control line signaling – Substation originated
Patent
1990-09-27
1993-08-10
Dwyer, James L.
Telephonic communications
Supervisory or control line signaling
Substation originated
379365, 379364, 379362, H04M 1274
Patent
active
052356353
ABSTRACT:
A keypad monitor which monitors the condition of a plurality of switches of a keypad is activated in response to receiving clock signals from an external clock source and is deactivated in the absence of the clock signals. The keypad monitor includes a key switch monitor which detects the closure of any one of the keypad switches to provide a first output signal, a clock detector for detecting the absence of the clock signals to provide a second output signal and any key down output logic which is responsive to the first and second output signals for providing an activation signal. The activation signal causes the external clock source to provide the keypad monitor with the clock signals for activating the keypad monitor.
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patent: 4489310 (1984-12-01), Trotyanetsky
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patent: 4929944 (1990-05-01), Nakajima
Advanced Micro Devices , Inc.
Dwyer James L.
Shehata M.
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