Communications: electrical – Digital comparator systems
Patent
1976-07-02
1977-10-25
Pitts, Harold I.
Communications: electrical
Digital comparator systems
340152R, H04Q 300
Patent
active
040558355
ABSTRACT:
Line-seizing circuitry is disclosed by which a plurality of remote terminals may be connected to a central data recorder over a single two-wire data line with only one terminal being in communication with the recorder at any one time. Tie-breaking circuitry is included to prevent two remote units from going onto the data line simultaneously. A current source is placed across the line and when any terminal goes on the line, a resistor is also placed across the line reducing the voltage thereon below a first voltage level; the other terminals sense that low voltage and are prevented from going on the line. Each terminal includes an oscillator and may go on line only during an output pulse of the oscillator. If two terminals should attempt to go on the line simultaneously, the voltage across the line is reduced below a second and lower voltage level, and both terminals are removed from the line. Each terminal then repeatedly attempts to go on line with every output pulse of its respective oscillator until the different frequencies of the separate oscillators causes one to go on the line a sufficient period of time prior to the second that the second is held off the line.
REFERENCES:
patent: 3691527 (1972-09-01), Yamamoto
patent: 3691528 (1972-09-01), Calvagna
IBM Tech. Discl. Bull., vol. 5, No. 10, Mar. 1963, pp. 57-58, R. L. Brady, "Cross Channel Switch."
Smiglee Jerome
Thornton Douglas R.
Manitou Systems, Inc.
Pitts Harold I.
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