Abstract: A first and second electronic devices are connected by two data lines arranged in a wired-AND configuration so that each device can signal the other device by forcing one of the two-wires into a "low" condition. An inventive method uses serial transfer of a predetermined numbers of bits in a digital word delimited by start and stop bits which are, in turn, defined by their relation to a clock signal on one of the data lines. The start and stop bits are chosen to be in a particular state during the "active" portion of the clock signal. Thus, the need for clocked gates or multivibrators is eliminated. In the preferred embodiment, the method and apparatus are used in a digital multimeter to intercouple a microprocessor and an electronic measuring circuit so that the microprocessor can control the measuring circuit and receive measured values from the circuit.

Abstract: An overvoltage protection circuit for a CMOS electronic multimeter circuit uses a pair of complementary field-effect protection transistors connected to each input line of the meter circuit. The gate electrodes of the protection transistors are connected to bias voltage sources which provide bias voltages with magnitudes slightly less than the meter power supply voltages. The protection transistors go into conduction when an overvoltage condition causes the voltage on the input to exceed the bias voltages and the conducting protection transistors clamp the input voltage to substantially the bias voltage. Current caused by an overvoltage condition is shunted to ground thereby avoiding a charging condition in the power supplies.

Abstract: A method and apparatus for scheduling operating sessions to be performed by a group of remotely controlled devices. A remote controller is used to operate the remotely controlled devices at selected times scheduled by the user. The operating sessions may be programmed to be performed on a daily or weekly basis without continued reprogramming by the user.

Abstract: A digital multimeter includes a microprocessor control and a keyboard input. The microprocessor functions to control the display of parameters measured by the meter and displays such measured parameters. The keyboard includes switches to allow the user to select a parameter which is desired to be measured as well as a range of values for that parameter for use in measuring parameters of a device under test connected to the multimeter. The microprocessor communicates with the keyboard and functions to control a resistor and switch network to configure the multimeter to test selected parameters within selected ranges. The multimeter incorporates an overload protection function which compensates for an over-large voltage on the input leads of the multimeter, thus preventing damage to the circuit and to the multimeter.

Abstract: A multimeter converts an input voltage into decibels. Preferably, the input voltage is converted into dbm. The multimeter includes a table of voltage values wherein each entry is associated with a given decibel value. The input voltage is compared with entries in the table to locate a first entry which is larger than the input voltage. A second entry having a lower value than the input voltage is then located in the table. A fractional value that is indicative of where the input voltage lies at a range between the first entry and the second entry is calculated using the first and second entries. The fractional value is added to a decibel value corresponding the second entry to produce a decibel value for the input voltage. The input voltage may be scaled down into an appropriate operational voltage range and then the calculated decibel value may be scaled up to compensate for this scaling down.

Abstract: An infrared remote-control system and method for the simultaneous transmission of data from two or more separate hand transmitters to a single remote-control receiver is disclosed. Interference between transmitted signals is eliminated by interlacing control signals with quiescent periods during transmission. The control signals are received and validated by the receiver based on the quiescent periods.

Abstract: A capacitance measuring circuit uses only a DC voltage source to perform the capacitance measurement. For this purpose, the circuit is arranged to charge an unknown capacitor which is being measured from a DC source and to discharge the capacitor through a constant current circuit such that the discharge voltage across the capacitor decreases linearly from its initial value to a predetermined, final value. The measurement circuit monitors the time taken by the capacitor to discharge in order to determine the capacitance value.

Abstract: Method and apparatus for effecting mode switching from a transmission mode to a command mode of an intelligent modem operatively coupled to a digital data device and a telephone line is disclosed. A termination of the modem's transmission mode is effected after a predetermined silent time interval in which no data is received from the device and prior to the transmission of additional data on the line. Operation of the modem switches to a buffer mode in which data sent from the device is temporarily stored instead of being transmitted on the telephone line. If the stored data is a proper escape sequence, operation of the modem switches to the command mode. If a proper escape sequence is not received, operation of the modem switches to a purge mode in which the stored data is transmitted on the telephone line. The apparatus comprises a data interface, a novel modem controller and a modem engine.

Abstract: A method and apparatus for editing video cassettes. The video cassette editor can be used to move a video cassette to a particular position on the tape relative to a reference point as a function of tape length expressed in units of time. The video tape editor is also capable of calculating recording speed switchover points for maximizing the recording time in standard play mode and thereby increasing the quality of the video image for the maximum amount of time.

Abstract: A remote controller capable of learning and later transmitting infrared signals transmitted by any other remote controller. The remote controller determines which of four modes of transmission a signal is transmitted in, including carrier mode, pulse mode, frequency shift keying mode and continuous wave mode. Once the type of signal is determined the controller learns each signal, saves them and later replays them to control a remote device.

Abstract: A method and apparatus for causing a remote controller to execute a sequence of instructions at a preprogrammed time. A remote controller includes a timer and may be used to turn on the various components of an electronic entertainment system including a recording device and to transmit a starting sequence which causes the recording device to record. After the selected duration of time expires the remote controller stops and recording device from recording and turns off the components of the system or causes other instructions to be performed.

Abstract: A remote controller capable of learning and later transmitting infrared signals transmitted by any other remote controller. The remote controller determines which of four modes of transmission a signal is transmitted in, including carrier mode, pulse mode, frequency shift keying mode and continuous wave mode. Once the type of signal is determined the controller learns each signal, saves them and later replays them to control a remote device.

Abstract: An interface circuit is disclosed for connecting a digital computer to a modem or other peripheral circuit through either a standard digital signal (RS232) "port" or an audio-frequency "port" normally used by the computer to store and retrieve information on audio-frequency magnetic tapes. The interface circuit allows the modem to be used economically with a small computer which does not have a standard RS232 "port". In order to allow the modem to connect to the audio-frequency "port" the interface circuitry combines filtered audio signals received by the modem from an associated telephone line with RS232 signals generated by the modem decoding circuitry to produce tone bursts which can be decoded by the computer audio-frequency port. The interface circuitry can accept either RS232 signals or tone bursts from the computer to be transmitted by the modem by automatically adjusting an internal threshold level.