Method for and apparatus for operating a local communications module in arbitrating for mastership of a data transfer across a back plane bus in industrial automation controller
First Claim
1. A method for operating a local communications module in arbitrating for mastership of a data transfer across a backplane bus, the method comprising the steps of:
- (a) asserting a wired-or arbitration strobe line on the backplane bus to initiate a competition between the local communications module and other modules connected to the backplane bus which are all contending for data transfer mastership of the backplane bus;
(b) asserting a local weight code onto a set of wired-or weight code lines on the backplane bus, the local weight code being encoded to uniquely identify the local communications module on the backplane bus;
(c) continuously examining an aggregate weight code obtained as a set of actual logic levels appearing on the wired-or weight code lines of the backplane bus, and determining if the local weight code is numerically less than the aggregate weight code;
(d) if the examination performed in step (c) indicates that the local weight code is numerically less than the aggregate weight code, then releasing the weight code lines and the arbitration strobe line;
(e) if the examination performed in step (c) indicates that the local weight code is numerically at least as great as the aggregate weight code, then maintaining assertion of the local weight code on the weight code lines and maintaining assertion of the arbitration strobe line;
(f) releasing the arbitration strobe line after a predetermined time period following the assertion thereof in step (a); and
(g) monitoring for termination of the competition as indicated by release of the wired-or arbitration strobe line by all modules on the backplane bus, and thereupon latching an indication that the local communications module is awarded data transfer bus mastership for a succeeding data transfer cycle if the continuous examination performed in step (c) indicates that the local weight code is numerically at least as great as the aggregate weight code.
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Accused Products
Abstract
A bus structure for interconnecting the modules of an industrial automation controller includes DATA lines and associated control lines that enable interface circuits on each module to send and receive frames of data. An arbitration circuit in each module employs arbitration lines in the bus structure to conduct a two phase competition to determine which module receives the next bus mastership. The arbitration lines include a set of wired-or weight code lines and a single arbitration strobe line. Modules desiring control of the bus structure assert a local weight code onto the weight code lines and determine which module is asserting the numerically greatest local weight code. Arbitration is conducted separately on the bus structure and a winning module is ready to transfer its data frame as soon as the previous winner completes its transfer and relinquishes control of the bus structure. The winning weight code identifies both the source address of the winning module and the priority of the data frame to be sent, and is latched by all modules on the backplane bus as an arbitration vector to provide advance identification of the next module to transmit and the priority of the message.
82 Citations
18 Claims
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1. A method for operating a local communications module in arbitrating for mastership of a data transfer across a backplane bus, the method comprising the steps of:
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(a) asserting a wired-or arbitration strobe line on the backplane bus to initiate a competition between the local communications module and other modules connected to the backplane bus which are all contending for data transfer mastership of the backplane bus; (b) asserting a local weight code onto a set of wired-or weight code lines on the backplane bus, the local weight code being encoded to uniquely identify the local communications module on the backplane bus; (c) continuously examining an aggregate weight code obtained as a set of actual logic levels appearing on the wired-or weight code lines of the backplane bus, and determining if the local weight code is numerically less than the aggregate weight code; (d) if the examination performed in step (c) indicates that the local weight code is numerically less than the aggregate weight code, then releasing the weight code lines and the arbitration strobe line; (e) if the examination performed in step (c) indicates that the local weight code is numerically at least as great as the aggregate weight code, then maintaining assertion of the local weight code on the weight code lines and maintaining assertion of the arbitration strobe line; (f) releasing the arbitration strobe line after a predetermined time period following the assertion thereof in step (a); and (g) monitoring for termination of the competition as indicated by release of the wired-or arbitration strobe line by all modules on the backplane bus, and thereupon latching an indication that the local communications module is awarded data transfer bus mastership for a succeeding data transfer cycle if the continuous examination performed in step (c) indicates that the local weight code is numerically at least as great as the aggregate weight code. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An arbitration circuit which forms a part of a local communications module for arbitrating data transfer mastership of a backplane bus, the arbitration circuit comprising:
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an arbitration timing circuit for asserting a competition signal, which is connected through an open-ended driver to a wired-or arbitration strobe line on the backplane bus to initiate a competition between the local communications module and other modules connected to the backplane bus which are all contending for data transfer mastership of the backplane bus; a comparison circuit which includes a set of open-ended drivers for asserting a local weight code onto a set of wired-or weight code lines on the backplane bus, the local weight code being encoded to uniquely identify the local communications module on the backplane bus, and in which the comparison circuit continuously compares the local weight code to an aggregate weight code obtained as a set of actual logic levels appearing on the wired-or weight code lines of the backplane bus, the comparison circuit activating an output signal if the local weight code is numerically at least as great as the aggregate weight code and discontinuing assertion of the local weight code onto the weight code lines if the local weight code is numerically less than the aggregate weight code; and a detector circuit connected to the competition signal and the output signal from the comparison circuit, the detector circuit producing an ownership signal to the local communications module to indicate award of data transfer bus mastership for a succeeding data transfer cycle if the output signal from the comparison circuit is activated when the competition signal is deactivated. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method for establishing data transfer bus mastership amongst a plurality of modules connected to a backplane bus, the method comprising the steps of:
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(a) asserting a wired-or arbitration strobe line on the backplane bus by one or more of said plurality of modules which are contending for data transfer bus mastership; (b) asserting a local weight code onto a set of wired-or weight code lines on the backplane bus by each of said modules which are contending for data transfer bus mastership, the local weight code being encoded by each separate module to uniquely identify said each separate module on the backplane bus; (c) continuously examining an aggregate weight code obtained as a set of actual logic levels appearing on the wired-or weight code lines of the backplane bus by each of said modules which are asserting their respective local weight codes, wherein each of said modules separately determine if the respective local weight code is numerically less than the aggregate weight code; (d) releasing assertion of the arbitration strobe line and local weight codes by each of said modules which are contending for data transfer bus mastership if the examination performed in step (c) indicates that the respective local weight code is numerically less than the aggregate weight code; (e) maintaining assertion of the arbitration strobe line and the local weight code on the weight code lines by each of said modules which are contending for data transfer bus mastership if the examination performed in step (c) indicates that the local weight code is numerically at least as great as the aggregate weight code; (f) releasing the arbitration strobe line after a predetermined time period following the assertion thereof in step (a) by each of said modules which are continuing assertion of the arbitration strobe line and local weight codes; and (g) when the wired-or arbitration strobe line is released by all modules on the backplane bus to terminate the competition, latching an indication that the data transfer bus mastership for a succeeding data transfer cycle is awarded within the single module which asserted the numerically highest local weight code and thus was the only module remaining in the competition at the end thereof. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification