Display of input signals

摘要

In order to display signals, particularly to display the status of these signals when those signals are input to a programmable logic controller, the value of each input signal is monitored in a predetermined sequence of read operations. An output signal of a first value is generated if the value of the input signal is at a predetermined value at the time of the read operation or has been at that predetermined value in the time since the immediately preceding read operation. An output signal of a second value is generated if neither of these conditions applies. Different display indicators are thus generated when the first and second output signals are generated. This enables the display to give an accurate indication of the status of the signals. <IMAGE>