Hi All,

I was recently faced with the issue of being unable to download the charts to the PLC, due to Local Data Requirements being larger than the local stack configured. (PCS7 V8.2) After doing some research in the forum, it sounded like it was because I had used too many temporary variables. (Which was very possible, since I was doing some reporting work.) I considered reassigning memory in the H/W config, but decided against it, as it would've required a full CFC compile and download.

On further investigation, I found the culprit to be a string handling block, "LEFT", that I found under the Standard Library. The block's function is to return x amount of characters starting from the left of a string. Just by dragging 12 of these blocks into the charts had depleted all my local data.

However, if I make my own FB, and then call the "LEFT" command from within it, this new FB can be used in the charts with no effect on the local data requirements at all.

So are some blocks not meant to be called directly from the charts?

And secondly, I know I can see how much local data is being used from the chart reference data, but is there any way to determine what exactly is currently using up the local data?

Thanks to anyone who can provide some insight,

Gary

Hi Oreca,

Thanks for trying to explain, it still doesn't fully make sense though.

If i check the properties of this "LEFT" block, it says it uses 8bytes of local data, but if I drag just one of those blocks into the charts and compile, my local data requirements increase by 260 bytes.

Whereas my FB that I created that calls the "LEFT" block, says it needs 20 bytes local data, but when I drag it onto the charts and compile, the local data requirements don't change at all.