| 摘要 |
<p>A circuit for preventing the automatic operation of the time-out portion of a tone-to-pulse converter until after the first DTMF digit is dialed is disclosed. When a calling party goes OFF HOOK, the forward loop current flowing in the tip and ring in leads is sensed. The sensed current creates a binary zero signal that sets a latch circuit. The latch circuit inhibits the automatic operation of the time-out portion of the tone-to-pulse converter until the latch circuit is reset. The latch circuit is normally reset by the first output of the tone-to-pulse converter adapted to create a rotary dial-type pulse. Alternatively, going ON HOOK without creating a DTMF digit resets the latch circuit, as does the occurrence of a rotary dial pulse on the tip and ring in leads.</p> |
