The Q-Series PLCs support the facility to FORCE I/O but it is not always clear how to find out what has been forced if a PLC has been left in this state. It is not good practice to leave a LC with forced I/O but it is possible that this could happen. This document details how to find what has been forced and thus corrective action can be taken.

Design Constraints

Within GX IEC Developer it is possible to force I/O by simply double clicking the item in question while monitoring the code and change the state of the selected item. For example, Input X0 could currently be “OFF” but then forced to “ON” by the process described above. [NOTE, this is not the same as using the “Forced Input Output Registration/Cancellation” feature.] If an input is left in a forced state, there is no obvious indication that anything is forced. GX IEC Developer supports a feature called Entry Data Monitor that can be used to show forced status information as shown below.

The example above shows X0 being forced and Entry Data Monitor showing this status.

Entry Data Monitor can be found under the Online menu. Once Entry Data Monitor is on screen, you can right-click to get a floating menu, and then select Setup. From Setup you can then right-click one of the spare field positions (position 4 in the example below), and select the Field List. Finally, from the Field List you can select Status.

When you return to the main Entry Data Monitor screen you now have the status field shown above.

This obviously only gives details of the I/O that has been selected within Entry Data Monitor but if you right-click in Entry Data Monitor and then select from the floating menu Insert Forced Inputs, you will get a list of all the forced items as shown below.

Further Information

For further information, please refer to the GX IEC Developer manuals.

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