Preemptive bid communication system

Claim 2

A bus communication system comprising: (a) a unidirectional transmit bus and a receive bus coupled to one another such that information packets leaving said transmit bus are placed on said receive bus; (b) a plurality of interface units (BIUs) coupled to each of said transmit and receive buses at spaced locations along said buses; said BIUs communicating with one another by transmitting information packets on said transmit bus and receiving transmitted information packets from said receive bus; (c) each of said BIUs periodically obtaining a user information packet to be transmitted and each respective BIU operating; (1) in a free mode wherein transmission of said user information packet is initiated substantially immediately when said each respective BIU determines both of said buses are idle, but aborted if said each respective BIU concurrently detects energy on said transmit bus from an upstream BIU; (2) in a preemptive mode, after having aborted transmission of said user information packet, by initiating a respective communication period each time a complete information packet is received from said receive bus, transmitting energy on said transmit bus during each said respective communication period, and retransmitting the aborted packet after termination of a respective communication period during which energy is not received on said transmit bus from an upstream BIU, each said respective BIU operating in said preemptive mode from the instant transmission of said user information packet is aborted until retransmission of said aborted information packet is successfully completed, said communication period equal to at least the maximum signal propagation time along both said buses; and (3) in a captive mode, during which transmission of a user information packet from said each respective BIU is precluded, extending from the instant said each respective BIU has successfully transmitted a user information packet until both buses have been inactive for a communication period following the receipt of a complete information packet by said each respective BIU and for a captive period immediately thereafter, said captive period equal to at least the maximum signal propagation time along both said buses.

Claim 3

The system of claim 1, wherein said communication period and said captive period are each respectively equal to the maximum signal propagation time along both said buses.

Claim 4

The system of claim 1, wherein said each respective BIU switches from said captive mode to said free mode after a predetermined interval which is greater than said captive period even if said buses have not been inactive first for said communication period and then for said captive period.

Claim 5

The system of claim 1, wherein said each respective BIU is determined to have successfully completed transmission of its user packet when it has received from said receive bus the entire user packet it has transmitted.

Claim 6

The system of claim 1, wherein each of said user information packets is assigned either a first or a second priority, and wherein said each respective BIU operates in said preemptive mode and transmits its user information packet immediately after termination of a communication period during which it does not receive energy on said transmit bus from an upstream BIU whenever its user information packet to be transmitted is a first priority packet even if transmission of said first priority packet has not previously been aborted.

Claim 7

The system of claim 1, wherein transmission of a user information packet from said respective BIU operating in a free mode is precluded, from the instant said each respective BIU aborts transmission until termination of a respective communication period during which energy is not received, said each respective BIU operating in a free mode initiating said respective communication period each time a complete information packet is received from said receive bus.

Claim 8

A bus communication system, comprising: (a) a unidirectional transmit bus and a receive bus coupled to one another such that information packets leaving said transmit bus are placed on said receive bus; (b) a plurality of bus interface units (BIUs) coupled to each of said transmit and receive buses at spaced locations along said buses; said BIUs communicating with one another by transmitting information packets on said transmit bus and receiving transmitted information packets from said receive bus; (c) each of said BIUs periodically obtaining a user information packet to be transmitted, said user information packet having either a first or a second priority, each respective BIU operating: (1) in a free mode wherein transmission of said user information packet is initiated substantially immediately when said each respective BIU determines both of said buses are idle, but aborted if said each respective BIU concurrently detects energy on said transmit bus from an upstream BIU; (2) in a preemptive mode, after having aborted transmission of said user information packet, by initiating a respective communication period each time a complete information packet is received from said receive bus, transmitting energy on said transmit bus during said respective communication period and retransmitting the aborted information packet after termination of a respective communication period during which energy is not received on said transmit bus from an upstream BIU, said each respective BIU operating in said preemptive mode both from the instant transmission of said user information packet is aborted and when said user information packet is a first priority packet, said each respective BIU continuing to operate in said preemptive mode until it has successfully completed transmission of its user information packet, said communication period equal to at least the maximum signal propagation time along both said buses; and (3) in a captive mode, during which transmission of a user information packet from said each respective BIU is precluded, extending from the instant said each respective BIU has successfully transmitted a user information packet until both buses have been inactive for a communication period following receipt of said information packet completely by said each respective BIU and for a captive period immediately thereafter, said captive period being at least as long as the time it takes for a signal to propagate along both buses.

Claim 9

A bus communication system, comprising: (a) a unidirectional transmit bus and a receive bus coupled to one another such that information packets leaving said transmit bus are placed on said receive bus; (b) a plurality of bus interface units (BIUs) coupled to each of said transmit and receive buses at spaced locations along said buses; said BIUs communicating with one another by transmitting information packets on said transmit bus and receiving transmitted information packets from said receive bus; (c) each of said BIUs periodically obtaining a user information packet to be transmitted, said user information packet having either a first or a second priority, each respective BIU operating: (1) in a free mode wherein transmission of said user information packet is initiated substantially immediately when said each respective BIU determines both of said buses are idle, but aborted if said each respective BIU concurrently detects energy on said transmit bus from an upstream BIU; (2) in a preemptive mode, after having aborted transmission of said user information packet, by initiating a respective communication period each time a complete information packet is received from said receive bus, transmitting energy on said transmit bus during said respective communication period and retransmitting the aborted information packet after termination of a respective communication period during which energy is not received on said transmit bus from an upstream BIU, said each respective BIU operating in said preemptive mode both from the instant transmission of said user information packet is aborted and when said user information packet is a first priority packet, said each respective BIU continuing to operate in said preemptive mode until it has successfully completed transmission of its user information packet, said communication period equal to at least the maximum signal propagation time along both said buses; and (3) in a captive mode, during which transmission of a user information packet from said each respective BIU is precluded, extending from the instant said each respective BIU has successfully transmitted a user information packet until both buses have been inactive for a communication period following receipt of said information packet completely by said each respective BIU and for a captive period immediately thereafter, said captive period being at least as long as the time it takes for a signal to propagate along both buses.

Claim 10

The system of claim 7, wherein said communication period and said captive period are each respectively equal to the maximum signal propagation time along both said buses.

Claim 11

The system of claim 7, wherein said each respective BIU switches from said captive mode to said free mode after a predetermined period of time greater than said captive period even if said buses have not been inactive first for said communication period and then for said captive period.

Claim 12

The system of claim 7, wherein each respective BIU is determined to have successfully completed transmission of its user packet when it has received from said receive bus the entire user packet it has transmitted.

Claim 13

The system of claim 7, wherein transmission of a user information packet from said each respective BIU operating in a free mode is precluded, from the instant said each respective BIU aborts transmission until termination of a respective communication period during which energy is not received, said each respective BIU operating in a free mode initiating said respective communication period each time a complete information packet is received from said receive bus.

Claim 14

A bus communication system, comprising: (a) a unidirectional transmit bus and a receive bus coupled to one another such that information packets leaving said transmit bus are placed on said receive bus; (b) a plurality of bus interface units (BIUs) coupled to said transmit and receive buses at space locations along said buses, said BIUs communicating with one another by transmitting information packets on said transmit bus in receiving transmitted information packets from said receive bus; (c) each of said BIUs periodically obtaining a user information packet to be transmitted and each respective BIU operating: (1) in a free mode wherein transmission of said user information packet is initiated substantially immediately when either (a) both said buses are idle and the last information packet received by said each respective BIU was not involved in a conflict between two information packets or (b) both said buses have been inactive for a communication period immediately followed by a captive period wherein both periods are equal to at least the maximum signal propagation time along both said buses, and wherein the last information packet received by said each respective BIU was involved with a conflict with another information packet, said free mode being further characterized by the abortion of said information packet if said each respective BIU concurrently detects energy on said transmit bus from an upstream BIU; (2) in a preemptive mode, after having aborted transmission of said user information packet, by initiating a respective communication period each time a complete information packet is received from said received bus, transmitting energy on said transmit bus during each said respective communication period, and retransmitting the aborted packet after termination of a respective communication period during which energy is not received on said transmit bus from an upstream BIU, said each respective BIU operating in said preemptive mode from the instant transmission of said user information packet is aborted until retransmission of said aborted information packet is successfully completed, said communication period equal to at least the maximum signal propagation time along both said buses; and (3) in a captive mode, during which transmission of a user information packet from said each respective BIU is precluded, extending from the instant said each respective BIU has successfully transmitted a user information packet until both buses have been inactive for a communication period following receipt of an information packet completely by said each respective BIU and for a captive period immediately thereafter, said captive period being at least as long as the time it takes for a signal to propagate along both buses.

Claim 15

A bus communication system, comprising: (a) a unidirectional transmit bus and a receive bus coupled to one another such that information packets leaving said transmit bus are placed on said receive bus; (b) a plurality of bus interface units (BIUs) coupled to said transmit and receive buses at space locations along said buses, said BIUs communicating with one another by transmitting information packets on said transmit bus in receiving transmitted information packets from said receive bus; (c) each of said BIUs periodically obtaining a user information packet to be transmitted and each respective BIU operating: (1) in a free mode wherein transmission of said user information packet is initiated substantially immediately when either (a) both said buses are idle and the last information packet received by said each respective BIU was not involved in a conflict between two information packets or (b) both said buses have been inactive for a communication period immediately followed by a captive period wherein both periods are equal to at least the maximum signal propagation time along both said buses, and wherein the last information packet received by said each respective BIU was involved with a conflict with another information packet, said free mode being further characterized by the abortion of said information packet if said each respective BIU concurrently detects energy on said transmit bus from an upstream BIU; (2) in a preemptive mode, after having aborted transmission of said user information packet, by initiating a respective communication period each time a complete information packet is received from said received bus, transmitting energy on said transmit bus during each said respective communication period, and retransmitting the aborted packet after termination of a respective communication period during which energy is not received on said transmit bus from an upstream BIU, said each respective BIU operating in said preemptive mode from the instant transmission of said user information packet is aborted until retransmission of said aborted information packet is successfully completed, said communication period equal to at least the maximum signal propagation time along both said buses; and (3) in a captive mode, during which transmission of a user information packet from said each respective BIU is precluded, extending from the instant said each respective BIU has successfully transmitted a user information packet until both buses have been inactive for a communication period following receipt of an information packet completely by said each respective BIU and for a captive period immediately thereafter, said captive period being at least as long as the time it takes for a signal to propagate along both buses.

Claim 16

The system of claim 12 wherein said communication period and said captive period are each respectively equal to the maximum signal propagation time along both said buses.

Claim 17

The system of claim 12, wherein said each respective BIU switches from said captive mode to said free mode after a predetermined period of time greater than said captive period even if said buses have not been inactive first for said communication period and then for said captive period.

Claim 18

The system of claim 12, wherein said each respective BIU is determined to have successfully completed transmission of its user packet when it has received from said receive bus the entire user packet it has transmitted.

Claim 19

The system of claim 12, wherein each of said user information packets is assigned either a first or a second priority, and wherein said each respective BIU operates in said preemptive mode and transmits its user information packet immediately after termination of a communication period during which it does not receive energy on said transmit bus from an upstream BIU whenever its user information packet to be transmitted is a first priority packet even if transmission of said first priority packet has not previously been aborted.

Claim 20

The system of claim 12, wherein transmission of a user information packet from said each respective BIU operating in a free mode is precluded, from the instant said respective BIU aborts transmission until termination of a respective communication period during which energy is not received, said each respective BIU operating in a free mode initiating said respective communication period each time a complete information packet is received from said receive bus.

Claim 21

A bus interface unit (BIU) for data communication systems wherein information packets are periodically placed on and removed from a bus, comprising: (a) control means; (b) energy detect means coupled to said control means for detecting energy on said bus and for signalling said control means when energy is detected on said bus; (c) first timer means coupled to said control means for providing a time interval corresponding to a captive period; (d) second timer means coupled to said control means for providing a time interval corresponding to a communication period; (e) transmitter means coupled to said control means for generating energy during said communication period, wherein said energy is to be placed on said bus during said communication period, and wherein the amount of energy generated is at least that necessary for detection by another BIU but is substantially less than that necessary to transmit an information packet; and (f) memory means coupled to said control means for storing information packets removed from said bus and for storing information packets to be placed on said bus.

Claim 22

A bus interface unit (BIU) for data communication systems wherein information packets are periodically placed on and removed from a bus, comprising: (a) control means; (b) energy detect means coupled to said control means for detecting energy on said bus and for signalling said control means when energy is detected on said bus; (c) first timer means coupled to said control means for providing a time interval corresponding to a captive period; (d) second timer means coupled to said control means for providing a time interval corresponding to a communication period; (e) transmitter means coupled to said control means for generating energy during said communication period, wherein said energy is to be placed on said bus during said communication period, and wherein the amount of energy generated is at least that necessary for detection by another BIU but is substantially less than that necessary to transmit an information packet; and (f) memory means coupled to said control means for storing information packets removed from said bus and for storing information packets to be placed on said bus.

Claim 23

A BIU as in claim 18 further comprising third timing means coupled to said control means for providing a wait-time period wherein said wait time period is substantially greater than said communication period.

Claim 24

A BIU as in claim 18 further comprising detection means having an input adapted to be coupled to said bus and an output coupled to said second timer means for initiating the start of said communication period.

Claim 25

A BIU as in claim 18 wherein said transmitter means comprises counter means having an output coupled to said bus for counting a predetermined number of cycles of a system clock signal and providing an output signal representative of the number of cycles counted.

Claim 26

A BIU as in claim 21 wherein the number of cycles of the system clock adapated to be counted is substantially less than the length of an information packet.

Claim 27

A BIU as in claim 18 wherein said energy detect means comprises: (a) amplifying means having an input adapted to be coupled to said bus and an output, for amplifying energy detected on said bus; and (b) triggering means having an input coupled to the output of said amplifying means and an output coupled to said control means, for indicating the presence of energy on said bus.

Claim 28

A BIU as in claim 18 wherein said control means comprises a microprocessor.

Claim 31

The method of claim 25 further comprising: (a) initiating a communication period immediately after receipt of any information packet from said receive bus; and (b) transmitting an energy packet on said transmit bus during said communication period whenever said supplying of said information packet was previously aborted and said supplying BIU is operating in other than said captive mode.

Claim 32

The method of claim 26 further comprising supplying said previously aborted information packet to be transmitted on said transmit bus when no energy is detected on said transmit bus during said communication period.

Claim 33

The method of claim 26 wherein said communication period is at least equal to the time for the leading edge of a signal to propagate along the entire length of both said transmit and said receive buses.

Claim 34

The method of claim 26 wherein said energy packet is substantially shorter in duration than any information packet.

Claim 35

The method of claim 29 wherein said energy packet is one-half byte long.

Claim 36

The method of claim 25 further comprising reverting from said captive mode to said free mode after a predetermined interval.

Claim 37

The method of claim 31 wherein said predetermined interval is greater than the time for the leading edge of a signal to propagate along the entire length of both said transmit and said receive buses.

Claim 38

The method of claim 26 further comprising reverting from said captive mode to said free mode when no energy is detected on both said transmit bus and said receive bus during said communication period and during a captive period immediately following said communication period.

Claim 39

The method of claim 33 wherein said captive period is at least equal to the time for the leading edge of a signal to propagate along the entire length of both said transmit and said receive buses.

Claim 40

The method of claim 26 further comprising: (a) assigning a first priority to said information packet to be transmitted; and (b) transmitting an energy packet on said transmit bus during said communication period even when transmission of said information packet having a first priority assigned thereto has not previously been aborted.

Claim 41

The method of claim 26 further comprising reverting from said captive mode to said free mode after a predetermined interval.

Claim 42

The method of claim 36 wherein said predetermined interval is substantially greater than the time for the leading edge of a signal to propagate along the entire length of both said transmit and said receive buses.

Claim 43

The method of claim 25 further comprising: (a) initiating a communication period immediately after receipt of any information packet from said receive bus; (b) initiating a captive period immediately following said communication period; and (c) reverting from said captive mode to said free mode when no energy is detected on both said transmit bus and said receive bus during both said communication period and said captive period.

Claim 44

The method of claim 38, wherein said communication period is equal to zero when said any information packet was not involved in a conflict.

Claim 45

The method of claim 38, wherein said communication period and said captive period are each respectively equal to at least the maximum signal propagation time along both said buses.

Claim 46

The method of claim 38, wherein said communication period and said captive period are each respectively equal to the maximum signal propagation time along both said buses.