Northern Telecom Limited

Canai Computer and Network Architecture Inc.

David P Schenkel

David Milton

David MacDonald Delaney

Frank Mellor

Alastair A Warwick

Kenny Y Ng

A unidirectional bus data communication system which eliminates uncertainty as to the integrity of data received by a receiver connected to the bus, which data may have been involved in truncating collisions. A plurality of data stations are connected to a unidirectional bus which has segments connected to and between the stations. Each of the stations is connected to an upstream segment by a sense (S) lead and to a downstream segment by a transmit (T) lead. Each station is adapted to sense energy via its S lead arriving on an associated upstream segment of the bus and includes a transmitter for transmitting data signals via its T lead on an associated downstream segment of the bus. Signal delay elements interconnect upstream and downstream segments of the bus bypassing each of the stations. The time delay D of each of the signal delay elements is a function of the total interval of a predetermined group of data signal bit durations of the data signals added to a period T.sub.d which is equal to the time between arrival of energy at an S lead and the instant when an associated transmitting means can, in response to such detection, stop transmitting energy on its T lead.

System for implementing improved attempt-and-defer access contention

An apparatus and method of communicating data signals on a bus having an upstream portion to which transmitters of a plurality of station are connected, and a downstream portion to which receivers of the stations are connected, and to which an end station is connected having a transmitter connected more upstream than any of the plurality of stations. Signals to be transmitted from each of the plurality of stations are appended to the end of the data stream passing thereby. A bus clear signal is transmitted from the end station, along the bus. When any signal including the bus clear signal is detected from upstream at any of the plurality of stations that might be transmitting, transmission of signals from the plurality of stations is immediately terminated. Transmission of the bus clear signal from upstream thus clears the bus to allow for transmission of different priority signals on the bus.

Packet communication system and method of clearing communication bus

A bus system for exchanging information between a plurality of circuits connected to the system. The bus system includes a polling bus, a message bus, and a bus controller. The bus controller polls each circuit to see if the circuits require access to the message bus. Information between the circuits is conveyed by first transmitting the information to the bus controller where it is temporarily stored. That information is then sent to the destination circuit by the bus controller. Information is thus conveyed over the message bus twice for every exchange of informaton between two circuits.

Double transit bus system

Fault checking of slave devices. All the slave devices are polled periodically by a master control circuit and their reponse is noted. The master control circuit asserts a control signal for every other poll so as to cause the slave device to invert the bits in its response signal when the control signal is asserted. The non-inversion of the bits during the period of several polls is indicative of either a fault condition or a device not present condition.

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Ottawa, Canada

David P Schenkel