Abstract: A last number redial device which provides a valid dialing sequence/access code test, before the contents of a last number redial register are disturbed, is described. A first and a second register are alternately loaded with a first, threshold portion (N) of a telephone number (N+M) during a dialing sequence. The number of digits entered are counted. If the count is greater than a threshold amount (N+1), a toggle signal is produced indicating a valid number has been entered. A second, terminal portion of the telephone number produced during the dialing sequence is thereafter loaded to a third register. In this way, the entire number is loaded in the selected first or second register and the third register. If a last number redial sequence is initiated, the selected one of the first or second registers and the third register provide an output to the telephone line of the last dialed number.

Abstract: An energy management circuit for use in a telephone or other device which includes an electronic memory is disclosed. The invention provides a capacitive keep alive power supply to maintain said memory in an active condition during extended periods when the device is disconnected from a line power source, as in a telephone on-hook condition. A large capacitor charge is maintained within a predetermined voltage range during such disconnect conditions by a resistively coupled trickle charge power source. A comparator is operated to monitor capacitor charge and to produce a control signal when the voltage at the capacitor falls below a selected memory keep alive level. The control signal operates a switch to bypass the trickle charge circuit. The switch couples line power directly to the capacitor to charge the capacitor to a voltage sufficient to maintain memory contents intact. A switch inhibit circuit is provided to prevent trickle charge bypass during an inadequate or excessive line voltage condition.

Abstract: A last number redial device which provides a valid dialing sequence/access code test, before the contents of a last number redial register are disturbed, is described. A first and a second register are alternately loaded with a first, threshold portion (N) of a telephone number (N+M) during a dialing sequence. The number of digits entered are counted. If the count is greater than a threshold amount (N+1), a toggle signal is produced indicating a valid number has been entered. A second, terminal portion of the telephone number produced during the dialing sequence is thereafter loaded to a third register. In this way, the entire number is loaded in the selected first or second register and the third register. If a last number redial sequence is initiated, the selected one of the first or second registers and the third register provide an output to the telephone line of the last dialed number.