Dual function input/output for a programmable controller
First Claim
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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Accused Products
Abstract
The invention disclosed provides circuitry which is selectively operable either as an input point or as an output point in a programmable controller having multiple input and output points for exchanging signals between a central processing unit (CPU) of the controller and a process being controlled. Preferably, operation as an input point or as an output point is under control of the CPU. The invention includes a common input/output terminal for terminating both input and output devices; an input return terminal for terminating a return conductor from the input device; an output return terminal for terminating a return conductor from the output device; a preload resistor connected between the input/output terminal and the output return terminal so that a status signal is developed across the preload resistor indicating the status (generally, open or closed) of the input device; and an insulated gate transistor (IGT) connected between the input/output terminal and the input return terminal. The insulated gate transistor, capable of being triggered on and off, is held in an off state whenever the circuit is selected to be operated as an input point and is triggered on and off when the circuit is selected to operate as an output point. Most preferably, the IGT includes a main current section and an emulation current section and is arranged such that a burden resistor in series with the emulation section provides a diagnostic signal indicative of total IGT current.
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Citations
16 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. For use with a programmable controller having a central processing unit (CPU), an input/output circuit selectively operable under control of the CPU as an input circuit for receiving signals from an input device or as an output circuit for providing control signals to an output device, such circuit comprising:
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an input/output terminal providing a common termination point for said input and output devices; an input return terminal providing a return termination point for said input device; an output return terminal providing a return termination point for sad output device; preload means connected between said input/output terminal and said output return terminal, said means being responsive to said input device to provide a status signal indicatlve of the status of said input device; and an insulated gate transistor (IGT) connected, collector to emitter, between said input/output terminal and said input return terminal, said IGT being held in an off state whenever such circuit is selected to operate as an input crcuit and being turned on and off as necessary to provide power to said output device whenever such circuit is selected to operate as an output circuit. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification