Importance

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Abstract

A telephone device, typically a terminal, that receives a.c. communication signals and that sinks d.c. current to provide the off-hook signal is powered from (i) the telephone lines and, if line voltage is less than 7.4 v.d.c., from (ii) a 6 v.d.c. battery. Connection to telephone lines of voltage greater than 7.4 v.d.c. recharges the battery. The terminal further contains a CMOS microprocessor that may be declocked and placed in standby mode to conserve power. When so placed, the microprocessor maintains some of its signal lines at a logic High, 6 v.d.c., condition. In order to both unpower circuits such as a display, a memory, a DTMF dialer, and a modem to which the microprocessor signal lines connect, and to (ii) disrupt current leakage paths from the signal lines to ground through the unpowered circuits, the ground is removed from the circuits. This removal, controlled by a signal from the standby microprocessor, is performed by a transistor switch.

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First Claim