9.2 USER INPUT/OUTPUT

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9.2.1 Multiplexing

Large numbers of inputs and outputs tend to use PLCs inefficiently.

Consider the example of 16 buttons in a keypad. If we connect each button to an input, 16 inputs will be required. But, it is also possible to connect the buttons to 4 outputs and 4 inputs.

A similar multiplexing technique can be used for output, as is commonly done for LED digit displays. (Most red LED displays look constant, but they actually flicker at more than 30Hz).