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Old April 16th, 2021, 01:28 AM   #1
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Jieve is offline
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Control Logix: Forcing using HMI Pushbuttons


Controllogix 5572 with Studio 5000 v33 and FactoryTalk View SE v12. Is there a way to force I/O bits using HMI pushbuttons? I've tried to turn on forcing on particular input bits, and link them to pushbuttons as a standard tag, but that isn't working.

I could simulate the I/O I'm trying to force by changing the assigned inputs to regular bits that can be manipulated by HMI buttons, but was still curious if forcing is possible using HMI buttons.


Last edited by Jieve; April 16th, 2021 at 01:32 AM.
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Old April 16th, 2021, 03:15 AM   #2
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I'm sure someone will correct me, but I can't think that would be something possible to do from an HMI and not from a specific place in the processor. Mostly because there's two actions required (enable forces and force).

You could buffer the output and add an OR branch with the "force" command, but I'd still put some sort of protection to it like a key switch or password control.
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Old April 16th, 2021, 03:40 PM   #3
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"Forcing" as you call it, is NOT possible to do from the HMI.

The HMI cannot write to the forces data area, neither can the HMI "Enable" forces.

I/O Forces are reserved as commissioning/testing tools, and I doubt that will ever change.

Now let us sweep "Forces" under the carpet, where they belong, hidden from view unless you have the programming software.

I believe what you are trying to achieve is a way of turning inputs and outputs On and Off from the HMI. Yes, that can be done but indirectly. Which means there's a whole bunch of code behind it. Every single input and output has to handled according to its function, and there are many variants.

Inputs could be driven by normally-open or normally-closed contacts, but they could be "looked at" in the code with XIC or XIO. (4 permutations)

Outputs could be driven from an HMI bit, but do you want the output to come on, or go off.

Seems like you will have a lot of engineering thought to perform.
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Old April 16th, 2021, 04:32 PM   #4
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For outputs you can just create some standard Hand/Off/Auto code for each output.

For inputs as said above you can buffer them and then use the same Hand/Off/Auto logic to output the buffered input.
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Old April 17th, 2021, 03:45 AM   #5
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Originally Posted by Jieve
...Is there a way to force I/O bits using HMI pushbuttons?...
Just to officially rubber stamp the above advice...

ID: QA50205 | Access Levels: TechConnect
Enabling/disabling forces in the Logix controller programmatically

"Enabling and disabling forces programmatically in the controller are neither allowed nor supported operations."

"A little nonsense now and then is relished by the wisest men".
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Old April 17th, 2021, 12:06 PM   #6
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HOA Data Structures

I'm not familiar with all the Rockwell data structure stuff but I have a simple HOA bit pattern that I've used for years with different PLCs and interfaces. It's described in the PLC class outline download at It's around page 153. Some thought must be taken when determining where to located it with a register-based protocol. Let me know if you want to use it for something.

As others have suggested, true I/O forcing from an HMI would be a really scary thing.
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Old April 17th, 2021, 10:55 PM   #7
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You could create an array of bits that when toggled from the HMI will trigger retentative bits that contacts are either inhibiting or paralleled with your outputs to turn them on or off.
You are not using the force function but basically doing the same thing i believe.
Then monitor these retentative bits if in the "on" state the machine cannot start an automatic cycle, since any "on" state of these particular bits essential means a testing cycle or phase.
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