Hi,

please check this entry:

Programming Guideline for S7-1200/S7-1500

Regards,

Towome

Not trying to quote anything from those guidelines, but avoid using STRING.  Use STRING[xx] where xx is the largest length string that can ever be useful for that specific tag.

This is especially important for a string array.

Let's say the longest string a (1D) bar code reader can ever return valid bar code data is 85.

Now let's say the PLC needs to track the status of at item from the time it is first scanned through some hypothetical manufacturing plant.  Let's say that there are no more than 99 opportunities to scan an item once the item enters the initial tracking station - or maximum of 100 total bar code scans.

Definition:
  BarCode_DB:
    ScannedItems : Array[0..99] of STRING
      Uses 100*256 = 25600 Bytes work memory

Definition:
  BarCode_DB:
    ScannedItems : Array[0..99] of STRING[85]
      Uses 100*87 = 8700 Bytes work memory

Saves 16900 Bytes work memory

That is the kind of thinking you need to save some real work memory.

There are other ways, like using FBs and FCs and avoid duplicate code. 

You can read up on my prior posts on the subject, but it really is summed up in the quoted programming guidelines these days.  Back when I was in a memory crunch, s7-1200 PLCs had a very small amount of work memory - especially compared with today's S7-1200's with the latest firmware that yields an additional 25kB of work memory for the same PLC.

The same project I build 14 years ago with Firmware 1.x and filled up 3/4 through development fits within 60% of a s7-1215 using the techniques recommended by Siemens in those guidelines.

The tricks I had to use made for horrible code to maintain.  Every time I had to make a change, it affected nearly every block because I was forced to use global tags even in FBs and FCs and to not create truly abstract / reusable logic as a result.  I hated it, but it got delivered.  The first time I moved the code to a s7-1215, I started redoing the things that pushed the code over the limit like adding comments and longer tag names and pulling globals out of FBs and FCs which led to abstract FBs and FCs.

In the end, it made troubleshooting RS485 comms much easier to the point where that's the least problem, formerly the #1 problem by far.

Hopefully you do not attempt to follow in my 14-year ago footsteps just to save memory.  Get a bigger PLC work memory capacity, or do what we did and standardize on S7-1500's once they were fully capable of taking on everything we were doing with the 1200's - where practical of course.

StalinCode

Hi Towome!

I have already read this programming guideline, but sometimes, programmers have some personal tips that in practice are better than doing it otherwise. you know what I mean?

Anyway, thanks for the answer!!!!!

Towome

Hi,

please check this entry:

Programming Guideline for S7-1200/S7-1500

Regards,

Towome