Importance

Loading Importance Indicators...

Abstract

A telephone line monitoring circuit for a MODEM monitors the TIP and RING lines of the telephone line. A first circuit of the monitoring circuit detects when a local phone goes off-hook while the MODEM is on-hook by sensing a decrease in a differential voltage between the TIP and RING lines. A second circuit detects the pick up of a local phone while the MODEM is off-hook by detecting a change in the impedance between the TIP and RING lines. A third circuit detects the hang up of a remote phone connected with the MODEM while the MODEM is off-hook by detecting a temporary break in the DC loop between the central office and MODEM. A snoop circuit monitors the telephone line for DTMF signals while the MODEM is on-hook. The snoop circuit becomes AC coupled to the telephone line when enabled, and does not apply a significant load to the telephone line. The monitoring circuit permits a processor to control a variety of call-related functions, including the recording of incoming voice mail messages, the logging of incoming and outgoing calls, and the blocking of outgoing calls to specified telephone numbers.

Loading the Abstract Image...

First Claim