markshancock (Customer) asked a question.
We have a PLC program that in one part, forwards modbus commands to another controller.
See the screen shot below. Note in rung 2 and 4 C70 is showing as both rising and falling at the same time. I can't see how that should be possible.
C70 isn't "rising and falling" at the same time. What is happening is rung 2 is going true only when C70 is going true (and this happens for just one scan), while rung 4 is only true when C70 is going false (and this happens at one later scan).
But nothing set C70 false. See that only happens on rung 3 if DS9=5 which you can see is not true.
Yes, I agree that in rung 4, C70 is still on. So, why is the C70 falling edge sensor marked as true (light blue) since a falling edge only happens when C70 turns off - which it didn't.
The blue is to illustrate the status of the C70 address, meaning it's true. What it does not show is the actual status of the one-shot instructions. This is because one-shot rising - or falling - happen in one scan, so an attempt to show this would be almost futile.
I mean the light blue highlight indicates the state of the bit, not the state of the instruction. If it indicated a rising or falling edge, you would never see it. If I'm not mistaken.
Light blue should indicate the output of the operation - like the = operator. Yes, I know that if is transient and so will never show but showing it as light blue is inconsistent with how other operators work.
I have requested someone to capture the values of C59-C65 in case those could be a better way to not keep sending the command but handle a case when the command doesn't work (maybe that is what is causing the problem we are seeing)
The blue is to illustrate the status of the C70 address, meaning it's true. What it does not show is the actual status of the one-shot instructions. This is because one-shot rising - or falling - happen in one scan, so an attempt to show this would be almost futile.