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Blinking green lights after upload, online mode still works


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We've run into an issue we haven't been able to solve for a day or so. When we restart the PLC it loads up fine with the code that is already on there. We can even go online from unilogic and view the values. However, when we try to download code from unilogic onto the plc the modules all get stuck on blinking green lights. Restart the PLC and everything works as normal, just for some reason we cant update the code on there. We thought that maybe we had messed up the hardware config so we opened a previous version of our project and that didn't work either. Also since we were able to go online, the code we have open is matching what is on the PLC. We noticed the day this happened our trial ran out, so we activated it with a key. We don't know if that was part of the reason or just a coincidence, but I do believe it is activated now and the problem has not been fixed. Any help would be appreciated since we can't really progress when we can't update the code.

Update (
It downloads but we have to restart it for it to register. if we dont restart its stuck in initialization.

Thank you!

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What version of UniLogic are you using?

What version is the OS in the PLC?

If they are mis-matched, then downloads will not go thru until OS in PLC is updated.


There is no trial period for UniLogic.

The registration is just so Unitronics knows where it is installed and probably for the newer security requirements for windows programs.


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  • 1 month later...
  • MVP 2023

Confirm that you are using the correct cable (it's not the same cable as that used with the EX-A2X) and confirm that you are plugging the correct end of the cable to the module and the correct end to the PLC (the cable can only be oriented one way). Also, confirm that the I/O modules are identical, and in the same order, as in the hardware configuration in the PLC program.

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Thanks for you quick reply. Yes, cable is correct and plugged in the correct way. Yes, the modules are in same order in HW configuration as they are DIN rail.  I can download program to PLC but it's like the plc is not communicating with ex-a1.  I have branches off 0v supply to the ex-a1 and v570 - sounds like a longshot but could this be a cause? I originally connected v570 to ex-a1 with a regular cat5 patch cable. Could this have damaged the ex-a1?



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I have successfully connected to expansion modules through the ex-a1. 

I checked for updates in Visilogix and downloaded my program - it now works fine.  Thanks to all for your help. 

FYI... I am using an ordinary patch cable to connect v570 to ex-a1 - It will not work with the exl-cab295 cable


Thanks again


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