Rockwell Logix Emulate won't go to single scan

[patjdixon]

When I select Single Scan, nothing happens. The application continues to run. I expected it to stop scanning and execute on demand. Do I have to do something to make Single Scan work?

 

[JLand]

I had the same issue and stumbled across this thread.

If anyone happens across this with the same issue, my problem was I had my task set to periodic. For some reason, single scan doesn't work with periodic tasks and I had to convert mine to continuous. I did not test with event tasks, but I doubt it would work. This is on Logix Designer v32.11 with Logix Emulate v32.00.

I placed my emulated PLC in program mode (it doesn't matter from Designer or Emulate), right click the PLC from Emulate, press Single Scan. Then put the PLC in run mode (again, does not matter, but I find it easier from Emulate). One scan will execute. You will get a weird pop-up (you may have to hunt for the popup if you placed the controller in run mode from Designer) asking "RUN Continuously? NO Single Scans Again". Press "No" and another single scan will run again. Press "Yes" and the PLC will return to normal behavior (i.e. scanning continuously). The only way I was able to run just a single scan and not return the PLC back to normal was to ignore the popup (not pressing either button) and return the PLC back to program mode from Designer.

Good luck all and as always, thanks Rockwell for fantastic documentation.

 

[JaxGTO]

In the programming software you have to put the PLC in Run or Test Mode. Then you go to the Emulator and select Single Scan. It will perform one scan and then ask you if you want to "RUN Continuously/No Single Scans". If you don't want it to keep scanning don't press anything and go check your code. Every time you hit NO after that it does a single scan.

 

[patjdixon]

Wow, that is messed up! Continuous scan is not good, and even Rockwell warns you not to do it. Single scan for testing is a very important feature in order to figure out what is happening in a sequence of logic to see where things go wrong. The idea of having to change logic from periodic to continuous in order to debug is nutty.

Thank you very much for figuring this out.