US PATENT SUBCLASS 379 / 283
.~.~.~.~.~ Dual tone multifrequency (DTMF) receiver

Current as of: June, 1999
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379 /   HD   TELEPHONIC COMMUNICATIONS

242  DF  CENTRALIZED SWITCHING SYSTEM {15}
258  DF  .~ Switching controlled in response to called station addressing signal {9}
268  DF  .~.~ Having shared or common switching control {8}
280  DF  .~.~.~ Including registering or storing device for call address signal {7}
282  DF  .~.~.~.~ Voice frequency receiver {1}
283.~.~.~.~.~ Dual tone multifrequency (DTMF) receiver

DEFINITION

Classification: 379/283

Dual tone multifrequency (DTMF) receiver:

(under subclass 282) Subject matter in which the voice frequency receiver is responsive to the simultaneous occurrence of designated frequency pairs.