Abstract: A data bus system includes a plurality of serially connected active terminals configured to receive data and either retransmit the received data or transmit new data to the next adjacent terminal. The terminals are configured in a diagnostic mode to configure the system optimally at turn-on or in the event system faults occur, and are configured in a user access mode once optimum configuration is attained. The system is under control by one terminal at any one time during the diagnostic mode and any terminal is capable of being the control terminal. For operation in the user access mode a cyclic period is defined during which a portion of the period is set aside for synchronous transmissions and another portion of the period is set aside for asynchronous transmissions. Both synchronous and asynchronous users are thereby accommodated by the bus.

Abstract: An active data bus includes a plurality of multiplex terminals serially interconnected to form a closed loop. Each terminal is capable of assuming either a relay configuration wherein data received from a preceding terminal are retransmitted to a succeeding terminal or a transmit access configuration wherein the loop is opened at the terminal and locally-generated data are introduced therein. Each terminal is capable of functioning either in a diagnostic mode whereby system access is obtained by programmed action of the terminal's control microprocessor or in a user access mode whereby access is obtained without microprocessor action by virtue of hardware "capturing" an access window bit introduced by the last-accessing terminal. The last-accessing terminal functions to close the loop after introducing its data and before the access window has completely traversed the system. The access window is thereupon "trapped" on the closed loop and circulates until it is "captured" by the next accessing terminal.

Abstract: A data bus system includes a plurality of interconnected active terminals, i.e., terminals which receive data from one terminal and retransmit it or transmit new data to another terminal. The data is in serial digital form and is transmitted within a continuous series of time frames of predetermined length with each time frame being initiated by a control word transmitted by one of the terminals designated the controller terminal. Each terminal includes a counter which counts the bits between control words, and each control word includes an identification of the controller terminal so that each terminal can synchronize its counter with the counter at the controller terminal in accordance with the propagation time of data from the controller terminal. Logic circuitry is provided at each terminal so that one of a plurality of terminals can assume the function of the controller terminal should the presently designated controller terminal fail to generate control words to define the time frames.