AutoGen_6711249

I came across this when I was searching on how to do such a set/reset in SCL figuring there would be a ready to go instruction set. 

Decided to make something that functions in a similar manner with the logic and is relatively simple using two IFs. I'm not worried about memory constraints, so ELSIF isn't necessary for this (and makes it easier to read for troubleshooting).

REGION Simple Set/Reset Bit Example with Tank Level
//Permissives to Latch Bits
IF (NOT Estop.Bit AND HiTankAlarm.Bit) OR Set.Bit
THEN
         PumpRun.Bit := 1;
         Set.Bit := 1;
END_IF;

//Permissives to Unlatch Bits
IF (NOT Estop.Bit AND TankLevel >= TankSetPoint) AND Set.Bit
THEN
         Set.Bit := 1;
END_IF;
END_Region

Basically, the logic in the initial IF triggers the bit to be set while also being the last part to enable the “latching” secondary IF. Once the Tank Level is under the setpoint, the “latching” secondary IF drops out and the Pump will no longer run. 

Obviously test this properly, but with my initial testing it seems to work just fine. Using some similar logic with data logging events to great success, just haven't tested out this particular example (albeit real world is more complex with the permissives). 

After doing that, I'm rather fine with there not being a built-in instruction for Set/Reset in SCL as this can be applied relatively quickly and easily. Just would be nice for cleanliness when it comes to the code. 

1) Consider using the system words TRUE and FALSE instead of 1 and 0.
2) You are  missing a FALSE / 0 in your code.
3) You are using a very specific application example. What is the purpose of your posting?

I would invite you to use the search facility on this support site to find a public open-source library LGF (Library of General Functions). Therein are many sample pieces that are ready for use in your code but also learn from. A SR-latch is one of them.

1) Start using TRUE and FALSE. Your future self will thank you.

2) 

AutoGen_6711249

False is assumed as the assigned value goes back to False when not being told to be True.

That is not correct. What you are describing is not the function of OTL (load) and OTU (unload). You are describing the functionality of OTE (coil). Your code will not work as you intend it to. 

You can assign  Set.Bit := FALSE;  in the first code line if you want the behaviour you described. But then again, our view to your code is too limited to say what is needed. For that reason others will not find this discussion helpful.

3) Your posting is not helping someone else. It is application specific so that others will not follow what you have done. I bet you are having a problem and needs help to sort it out. If you need help, please do not hide it under the disguise of helping others.

It is good that you have found the library. I am sorry - I was wrong about the SR-latch being there. There are other public libraries that is worth looking at.

You mention OTL and OTR (OTU depending on which Rockwell software / hardware is used). Those are text representatives of LAD code. Those are not ST (Structured Text) instructions. ST is what most other manufacturers call SCL. 

The international specification for Structured Text does not have a Latch/Set and Unlatch/Reset instruction. You use assignment to TRUE and assignment to FALSE.

IMHO you should study difference between STAT and TEMP variables and use them accordingly.

Trying to use the LAD rules in SCL/ST will drive you nowhere.

AutoGen_6711249

False is assumed as the assigned value goes back to False when not being told to be True.