Nippon Electric Co., Ltd.

M/a-com Dcc, Inc.

Bob D Buschman

David Love

Daniel Raymond Wendling

Ronald T O'Connell

Deepak R Muzundar

Glenn D Muth

Pradeep P Kaul

Akira Miura

Thomas H Scholl

Michio Ikawa

Digitally encoded (DPCM) NTSC video is transmitted in a standard T3 data format and rate via a transmit interface module. The module is subjected to inputs comprising DPCM encoded NTSC video, horizontal sync and a video sampling clock at 3f.sub.sc, where f.sub.sc is the color subcarrier frequency. The sampling clock is used to write the DPCM encoded video and horizontal sync into a buffer. The buffer is read out via a read clock which is a submultiple of the 44736 MHz T3 rate. To assist in receiver decoding, the video data is supplemented with horizontal sync indicating code words, which designate the start of each horizontal scan line. On detection of a horizontal sync word read out of the buffer memory, the read clock is inhibited for the insertion of the horizontal sync indicating code words. The T3 frame is also supplemented with two digitized audio channels, stuff indicators and a stuff opportunity slot as well as parity, frame and multiframe indicators and an alarm channel. The T3 frame also carries data indicating a relationship between the T3 clock and f.sub.sc. This is useful at the receiver for ensuring that f.sub.sc at the receiver will track f.sub.sc at the transmitter. In accordance with standard T3 operation, the frame comprises 56 85-bit words, 28 odd and 28 even. The first bit of each 85-bit word is a control bit. Substantially all of the odd words include a 4-bit digitized audio nibble. Exceptions are two unused 4-bit nibbles, a single 4-bit stuff opportunity nibble and a single 4-bit video sample. Each of the even words includes 21 4-bit video samples which can be either video samples or sync indicating code words.

Interface apparatus and method for asynchronous encoding of digital

An electronic key telephone system is disclosed that provides a plurality of telephone features and functions, while only requiring a four-wire line between the central equipment and each key-set telephone (KST) and a two-wire line between the central equipment and each single-line telephone (SLT). Linear delta coding and time division multiplex (TDM) techniques are used to eliminate the multiple pairs required in traditional private business exchange (PBX) systems between the remote key telephones and the control unit. In the present system, a microprocessor controlled TDM controller transmits and receives control signals serially to and from interfaces in the system for control purposes and also for establishing exchange of digitized audio information data between selected interfaces. The system thus exchanges digitized audio information directly between interfaces and provides control signalling between the TDM controller and the interfaces, with all of the exchanges being done in real time. Among other things, the system is compatible with all types of existing central office exchange lines. The system may use combinations of single-line telephones (SLTs) or key-set telephones (KSTs). Specialized functions, such as conference calls, background music, external zone paging and night chime, as well as on-line maintenance, system configuration reprogramming, out-going telephone call control, and recordkeeping are available. To reduce complexity and increase economy, several functions in the system are time-shared, and the system is constructed in modular form to allow its capabilities to be tailored for its intended use.

Electronic key telephone system

Growing community of inventors

Gaithersburg, MD, United States of America

Bob D Buschman