How to run all ladders :huh:

Hello all,

I have a SLC 500 and I have been learning a lot.

Everything starts from LAD2

I have created a few more ladders:

LAD2 - MAIN
LAD3 - CAM
LAD4 - SLIDER
........

Using ladders allows me to organise the program and really focus on getting this right.

Here is the problem, which I think is simple however, I am not sure.

I know that sub routine must be used to jump between ladders. The issue is that LAD 3, 4, .... all work independently.

My question is, can you have all the ladder scanned at the same time. I would like to have about 40+ ladders and they all work independently with out the need of the other ladders.

I hope I am explaining it well.

Thank you

The ladders are scanned sequentially, ladder 2 is first, then the rest in the sequence that you select, once all your ladders are scanned, then the outputs are updated and the inputs are read and it all happens again.

You can use turn on the JSR to certain ladders if you want, I have seen programs in some machines that have multiple ladders depending an the machine mechanical configuration, so they select which ladders they run.

Alan.

Hello Alan,

Sorry to sound stupid. So you are saying that all the letters are scanned.

However, when I put some specific inputs and outputs in latter number three. They do not work. However if I put those same inputs and outputs in latter two they all work.

You need to call the ladder routines using a JSR instruction from the main ladder. It’s been a while since I’ve used 500 but it should be the JSR instruction, if not someone will chime in.

Either way you must tell it to run.

To scan other ladders than ladder 2 you need to use a JSR instruction, this can be conditional or not.

ladder 2 scans through until it gets to a JSR and it scans the new ladder and when it is finished with that ladder it then goes back to ladder 2 and continues until it gets to another JSR or to the end of the ladder, and the sequence starts again, after updating the outputs and inputs.

Alan.

Maxkling said:

You need to call the ladder routines using a JSR instruction from the main ladder. It’s been a while since I’ve used 500 but it should be the JSR instruction, if not someone will chime in.

Either way you must tell it to run.

Click to expand...

Perfect, thank you very much. Everything's working..

I used the latter number two and just put 2 x JSR going to the appropriate ladders.


Thank you very much

I typically use LAD 2 as my "Setup" ladder. It hosts all the JSR instructions for all other ladders.

As others have pointed out, a PLC will scan your logic in a very defined sequence: one rung at a time. In other words, it will start with rung 0000 in LAD 2, then it will go to rung 0001 in LAD 2, so on and so fourth. If a rung has a JSR instruction, the PLC will perform a simple jump to rung 0000 LAD x (where x is the reference from JSR).

On a second note: never feel dumb about your questions. We've all been there. It may seem obvious to many, but not to others. Don't hesitate to keep asking.

Hope that helps,
Vlad

Vlad Romanov said:

I typically use LAD 2 as my "Setup" ladder. It hosts all the JSR instructions for all other ladders.

As others have pointed out, a PLC will scan your logic in a very defined sequence: one rung at a time. In other words, it will start with rung 0000 in LAD 2, then it will go to rung 0001 in LAD 2, so on and so fourth. If a rung has a JSR instruction, the PLC will perform a simple jump to rung 0000 LAD x (where x is the reference from JSR).

On a second note: never feel dumb about your questions. We've all been there. It may seem obvious to many, but not to others. Don't hesitate to keep asking.

Hope that helps,
Vlad

Click to expand...

+1 to all of this.