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Force output with v570?


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  • MVP 2021

I just attempted to FORCE a digital output using a v570 connected to an I/O module. The output I selected was an unused output and thus had no ladder logic associated with it. While online with the PLC, I selected the output and then right-clicked on the Set/Reset button to select SET. The output would not turn on and the display in the eyeglasses column changed from 0 (zero) to this: 0<1>. What is the meaning of that display and why can't I Force an output?

By the way, the I/O module was clearly functioning as it had other outputs connected and they were operating properly according to the ladder logic turning them on and off.

The Help function had very little information, but did have a diagram which clearly showed forcing an Output. While writing software for the v570, I frequently need to force INPUTS and do so all the time with no issue, but this is the first time I've had occasion to need to force an OUTPUT. Is there something different about Outputs?

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  • MVP 2014

The output *should* be switching in this case.

I think it is time to check that all wiring and configuration settings are 100% correct. Which I/O module are you using? What numbered outputs are working correctly? Have you tried forcing some other outputs?

As a side note, if you select an unused output you can toggle it's value just with the normal set/reset functions, there is no need to use "force".

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  • 2 weeks later...
  • MVP 2021

Sorry for the delayed response. I appreciate the help. Here are the answers to Simon's questions:

I think it is time to check that all wiring and configuration settings are 100% correct. Which I/O module are you using?

Wiring and setting appear to be correct. I/O modules being used are:

EX-D16A3-TO16

IO-D16A3-RO16

IO-D16A3-RO16

IO-DI16

What numbered outputs are working correctly?

All the outputs work correctly when following the ladder logic in run mode. We had what appeared to be a failed relay that I wanted to troubleshoot. It was connected to the first I/O module and was the only output being used on that module. That module had a bunch of inputs and the other modules were also mostly fully utilized with both inputs and outputs. My intent was to connect the relay to another I/O module with an unused output and then see if I could force it on and off while online with the PLC.

Have you tried forcing some other outputs?

Yes, I tried several and got the same results with each. When an output showed "0", I would force the output to "SET", the glasses display would change to "0<1>", but the I/O module corresponding output would not be lit and the force pushbutton would still display that the output was off. If I forced the output back to zero ("RESET"), the glasses display remained the same: "0<1>".

As a side note, if you select an unused output you can toggle it's value just with the normal set/reset functions, there is no need to use "force".

I don't really understand this. An unused output has no coil in the ladder logic to set/reset (I do NOT want to add the coil and download the change to the PLC). Or perhaps we're just talking past each other - when I say "force", I am referring to the little box that pops up with the state of an operand when it is clicked in the ladder or in the operands section at the bottom of VisiLogic when online with the PLC. For regular operands (MBs), if the bit is off the pushbutton will say "SET" and when it is on the pushbutton will say "RESET". For Inputs and Outputs the pushbutton will say the same thing but it is "greyed out" and you have to right-click to select "SET" or "RESET" to force the Input or Output one way or the other.

By the way, forcing inputs this way works perfectly, but outputs give me the result I describe above.

Bottom line, what I need to understand is, am I correct in my understanding that I SHOULD be able to force an Output in the manner I'm describing? If so, what should I be looking at to try to understand why it does not work the way it should.

Thanks!

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  • MVP 2014

Quote

As a side note, if you select an unused output you can toggle it's value just with the normal set/reset functions, there is no need to use "force".

I don't really understand this. An unused output has no coil in the ladder logic to set/reset (I do NOT want to add the coil and download the change to the PLC). Or perhaps we're just talking past each other - when I say "force", I am referring to the little box that pops up with the state of an operand when it is clicked in the ladder or in the operands section at the bottom of VisiLogic when online with the PLC. For regular operands (MBs), if the bit is off the pushbutton will say "SET" and when it is on the pushbutton will say "RESET". For Inputs and Outputs the pushbutton will say the same thing but it is "greyed out" and you have to right-click to select "SET" or "RESET" to force the Input or Output one way or the other.

By the way, forcing inputs this way works perfectly, but outputs give me the result I describe above.

Bottom line, what I need to understand is, am I correct in my understanding that I SHOULD be able to force an Output in the manner I'm describing? If so, what should I be looking at to try to understand why it does not work the way it should.

Thanks!

To start with your last question, From my knowledge, you should be able to force outputs this way. I was able to do it.

On the question of clarification, you are doing what I would expect with the outputs. However I don't expect the normal SET/RESET button to be greyed out. If the output is unused in the ladder (has no coil attached0, then the normal SET/RESET button should work OK. It's only when the output is linked to a coil that the Force is important, so you can override the logic that is driving the coil.

Something is obviously not right. I would try two things:

* the usual check you have the latest version of Visilogic, if not, download and and update the PLC OS

* download a blank project to your PLC then download the real project again.

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