Ncr Corporation

Albert J Chanasyk

William Martin Belknap

Donald J Girard

Robert R O'Dell

A system for controlling the transfer of a data message over a common communication channel between a plurality of processing devices includes a MOS/LSI controller chip associated with each processing unit for constructing a message to be sent to a sending device acknowledging the receipt of the message and the validity of the message. Logic circuits are included which generate a predetermined sequence of two binary bits indicating the receipt of the message and the validity of the receiving message. The binary bits are framed by two other binary bits and the sequence repeated a predetermined number of times to construct an acknowledgment message. The controller chip further includes logic circuits for decoding the acknowledgment message.

Data transmitting and receiving apparatus

A system for controlling the flow of data over a common bus between a plurality of processing units is disclosed which preferably includes a MOS/LSI circuit controller chip associated with each processing unit for awarding priority of access to the common bus when two or more processing units attempt to simultaneously gain access to the common bus. A contention circuit located in each controller chip is responsive to the sensing of each bit in the address of its associated processing unit, and generates a plurality of transitions on the common bus during the time a binary one bit is sensed in the address and listens for the presence of any transition on the common bus during the time a binary zero is sensed in the address. Access to the common bus is lost when transitions are detected on the bus during the time a binary zero bit is sensed and acquired when no transitions have been detected at the completion of the sensing of the address of the requesting processing unit.

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Cambridge, OH, United States of America

Albert J Chanasyk