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Dual function input/output for a programmable controller

  • US 4,593,380 A
  • Filed: 06/04/1984
  • Issued: 06/03/1986
  • Est. Priority Date: 06/04/1984
  • Status: Expired due to Term
First Claim
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1. In a programmable controller having multiple input and output points for exchanging signals between a controlled process and a central processing unit (CPU) of the controller, circuitry selectively operable either as an input point or as an output point comprising:

  • an in/out terminal which is electrically common for both input and output connections;

    a pair of return terminals, one terminal of which is an input return terminal and one terminal of which is an output return terminal;

    preload means connected between said in/out terminal and said output return terminal, operative to provide a status signal indicative of the status of an input device connected between said common terminal and said input return terminal; and

    controllable switching means connected between said in/out terminal and said input return terminal, said switching means being operative to be switched on and off for controlling power to an output load connected between said in/out terminal and said output return when such circuitry is operative as an output point and to be held off for provision of said status signal when such circuitry is operative as an input point.

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