Colin Carpenter

IEC Developer Online Change rules

5 posts in this topic

Came across an issue yesterday that made me (once again) realise that I have no real idea about the rules regarding online changes when using IEC Developer 7.04.

We had to modify some code on a Q02 CPU that could not be stopped without a lot of grief, and it seemed simple enough, but proved a head scratcher.

Essentially we had one POU that contained numerous lines that allowed an operator to press an HMI GO button and, whatever he had selected from a drop down menu would set a bit on in the PLC.

Essentially, the raw code of that particular "rung" of the POU ended with 

LD  " go button"   AND "op1 requested"   PLS  "system bit"

and it was quite happy with that.

We wanted to use the system bit to SET a bit on, so the online change amounted to installing 2 extra lines, namely:

LD "system bit" SET "op1 flag"

Strangely, the online change of adding these two lines wasn't allowed as it said that it would need 530 lines to do the change????

I've found in the past that IEC seems to let you do large changes in POUs that are near the bottom of the "compiler table" but can struggle if the POU is high up, which I assume is related to the amount of lines of code beneath the change that have to be shifted down, but this is the first time I've seen such a tiny change cause issues.

We have set the "online changes to 2000 lines" in the options and know that his been downloaded in the past to the parameters,  but the CPU still seems to work to a 512 limit?

The work around was easy enough to do, but just left me realising that I still have no idea regarding the rules of online changes.

Any advice gratefully received ....



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There are a few things to take consider 

The format of the memory ( was MBOC checked) multiple block online change
Normally 500 steps are reserved when downloading for on-line change in a system Q but this can be changed.

If you have enough space in your PLC or a mem card you can download the whole program if you deselect parameters without having to stop the PLC.


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When you say MBOC, is that an checkbox option when you format the CPU memory to completely erase everything and re-format?

Have never fully understood the benefits or usage of a memory card in the PLC and have always just relied on the battery backed memory options until now.

Would you say that the benefits of a memory card are worth having as we are just installing a Q04 CPU and now would be a good time to add one if there are real benefits for future online changes etc.


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If you are using a 4 you are already using a universal type. So it automatically saves the program to the standard Flash Rom.
You are also working with GX Works 2 than instead of IEC Developer  so you can take full advantage of the file structure.
So an SD cards is not needed even though you can use a normal industrial SD card so costs would be low.



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Thanks .... we are using GX Works 2 so will have a detailed look.

Still puzzled by the Q02 and IEC Developer though ......

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