Abstract: A modem interface device is coupled to a computer such that the device is powered via a power signal received from a bus port of the computer, such as a Universal Serial Bus (USB) port, a RS-232 port, or a PS-2 port. The modem interface device has a telephone base connector, a modem connector, a power connector, a two-to-four-wire converter circuit, and a power distribution circuit. The two-to-four-wire converter circuit bidirectionally couples signals between the telephone base connector and the modem connector. The power distribution circuit receives electrical power from the power connector and supplies power to the two-to-four-wire converter circuit.

Abstract: A device for protecting a modem against harmful telephone line signals or reversed polarity telephone line signals includes a telephone line interface couplable to a telephone line, a modem interface couplable to a modem communication port, a measurement circuit that measures the value of an electrical parameter of a signal on the telephone line, an indicator circuit that provides an indication if the value of the parameter is not within predetermined limits, an isolation circuit that electrically isolates the modem communication port from the telephone line if the value of the parameter is not within predetermined limits, and a polarity detection circuit that determines the polarity of the telephone line with respect to the polarity of the modem communication port and reverses the polarities with respect to one another if they are opposite. Such operation of the apparatus may be initiated automatically in response to detection of an off-hook condition of the modem.

Abstract: An interface between an alternating voice-data (AVD) modem and a telephone that allows the modem to be connected to a PBX or office-type telephone system without using special software. The user speaks and listens through the telephone handset, which is disconnected from the telephone base and connected to the interface. The interface provides an impedance across the modem "Phone" connection. The impedance simulates the off-hook condition that would normally (i.e., when the modem is connected in the conventional manner to a non-PBX telephone) be provided by the non-PBX telephone and that, absent disabling the requirement by special software, the modem requires in order to properly switch between voice mode and data mode. The interface monitors the modem "Line" connection to detect whether the modem is in an off-hook state or an on-hook state. A compensation circuit minimizes attenuation of the wake-up tone by the impedance across the "Line" connection.