RSLGX5000 Move Instruction

[resistorboy23]

Hi all,

This is in Ladder logic...

This is a simple enough question. I am wondering if it is poor practice to place an OTE instruction after a MOV (all in series). In other words, is the 'output' connector of a MOV always TRUE as long as the MOV is being evaluated every scan?

My overall purpose is to convert a modicon 984 program. There are many 'SUB' instructions and I am finding I must use multiple Logix instructions to accomplish the same functionality.

 

[kekrahulik]

Will it work? Yes, Controllogix will handle it with no issues

Is it poor practice? In my opinion, yes. If you are confused as to whether it will work, then it is reasonable to think that others will likely be confused.

For those of us who grew up on PLC2's and PLC5's where this could not be done, it is confusing to see. Although I now fully understand it when I see it, I still take a short pause.

For what it's worth, I will say that placing multiple math instructions in series doesn't bother me and I will sometimes place multiple OTE's in series in order to view everything on one screen without needing to scroll down to see all the output branches. Placing an OTE after other output instructions hits me wrong. Placing anything after a timer or counter hits me wrong. Placing input instructions after output instructions really hits me wrong.

Just my opinions.

With that said, if you are converting a program, I would understand if you got the conversion done and working as is....with plans to clean it up once it is working.

 

[Operaghost]

The answer really depends on what you are doing. To some it is a poor practice, but in some instances, it makes perfect sense.

Here is an example of what it sounds like you are asking for, done three different ways but producing identical results. The real takeaway here is that your OTE is not in any way tied to the MOV. Look at my examples to see what I mean by that. They all produce the exact same result.

Plus I threw in another method that might be more of what you are actually looking for. Are any of them wrong? No. Are some easier to follow than others? Sure. I usually go by, what makes the most sense.

OG

 

[resistorboy23]

Thank you all for the replies! This is some good insight.

 

[xC0MMAND0x]

SPC Functionality - FTViewSE 7.0

-removed - sorry I meant to start new thread

 

[Ken Roach]

The first time I looked at a Modicon 984 program I was confused by the use of the SUB instructions.

In A-B, they're used to subtract one value from another.

In Modicon, they're multipurpose.

You can use them to subtract one value from another, and they are commonly used instead of a MOV instruction. When you subtract zero from a register, it just moves the original value to the register.

SUB instructions also have more than one output in the Modicon world; the output state depends on whether Value 1 or Value 2 is larger. So the SUB also works as a LES or GRT instruction.

Sometimes this is awesome, but sometimes it is confusing.

 

[ASF]

The other thing that confused the heck out of me when I first started looking at Modicon 984 programming was that it solved the networks vertically, not horizontally

As to the original question, I tend to put as much in series as possible rather than in parallel - because as kekrahulik said, you can see it all on the one rung and can therefore see more rungs on the screen at once. Particularly when I'm on site and only have a 13" laptop screen intsead of my dual 24" monitors

I was fortunate enough to be raised on CLX code, so it doesn't seem odd or unusual to me. But I can see how it would be if you'd been using SLC's for 20 years before CLX came along