Abstract: A data storage system comprised of a disk drive including a magnetic disk for storing an operating system program, a dynamic RAM memory circuit for temporarily storing the operating system program, a static memory circuit for temporarily storing customer entered data, and a direct memory access controller for periodically transferring the customer entered data from the static memory circuit to the magnetic disk and for transferring the operating system program from the magnetic disk to the dynamic RAM memory circuit in response to execution of a bootstrap or power-up program by the microprocessor. In the case of a power down during entry of customer entered data, the customer entered data is saved in the static memory and is transferred to the magnetic disk during the subsequent power up thereby avoiding the use of possibly corrupted data on the disk drive.

Abstract: A trunk circuit is disclosed for coupling a bidirectional lead pair, such as balanced tip and ring leads, to a pair of unidirectional leads such as unbalanced input and output leads. The trunk circuit incorporates a small inexpensive transformer for effecting this coupling and for providing large common mode signal isolation and correct longitudinal balance. Circuitry is provided for matching the nominal balanced AC and DC line impedances. The trunk circuit also provides circuitry for generating dial pulse signals under control of a microprocessor or other external controller.

Abstract: A digital progess tone detector, for connection to a telephone line and a PABX, comprising circuitry for generating one or more reference tones having user definable frequencies and performing single frequency discrete Fourier transforms on one or more signals received from the telephone line at the defined frequencies, and providing an output signal to the PABX in response thereto. The output signal provides an indication of whether or not a predetermined one or more progress tone frequencies have been detected in the received signals. Because the generated reference tone frequencies are user definable, the present invention can be easily adapted for use in various foreign countries having different progress tone frequency requirements. A preferred embodiment of the invention is implemented on a single microcomputer chip in conjunction with peripherals (such as codecs, crosspoint switches, etc.).

Abstract: A circuit for use in conjunction with a microprocessor for refreshing, checking and correcting data signals stored in a dynamic memory. The circuit utilizes a direct memory access controller for transferring data signals stored in successive locations of the dynamic memory to a non-existent peripheral. Data signals appearing on a data bus as a result of the data transfer, are applied to a parity checking circuit for generating an interrupt signal to the microprocessor in response to detection of parity errors in the data signal. The microprocessor then performs a data recovery routine in which correct versions of the data signal stored in a non-volatile memory, are transferred for storage in the dynamic memory under control of a microprocessor. Parity errors in data signals stored in the dynamic memory are thus corrected prior to being accessed by the microprocessor.

Abstract: A digital progress tone detector, for connection to a telephone line and a PABX, comprising circuitry for generating one or more reference tones having user definable frequencies and performing single frequency discrete Fourier transforms on one or more signals received from the telephone line at the defined frequencies, and providing an output signal to the PABX in response thereto. The output signal provides an indication of whether or not a predetermined one or more progress tone frequencies have been detected in the received signals. Because the generated reference tone frequencies are user definable, the present invention can be easily adapted for use in various foreign countries having different progress tone frequency requirements. A preferred embodiment of the invention is implemented on a single microcomputer chip in conjunction with peripherals (such as codecs, crosspoint switches, etc.).

Abstract: An apparatus and method of controlling the loop gain in a loudspeaking telephone comprising storing reduced representations of an outgoing signal and an incoming signal in corresponding incoming and outgoing storage circuits respectively, in which the storage circuits have much faster attack times than decay times, comparing the representations, and controlling the gains of outgoing and incoming signal paths of the loop according to the degree and polarity of the result of the comparison. With the outgoing signal path connected to a microphone or a signal source and the incoming signal path connected to a loudspeaker, hands-free communication can be carried on having much more natural characteristics than in the past, devoid of most of the "hollow" sound characteristic of prior art systems.