PLC-5 to Controllogix general practice question

Hi guys,

Doing a conversion from PLC5 to Controllogix, and so far it's going smoothly. The programs are fairly simple, the errors are minimal and straight-forward.

One recurring error is mismatched data types. The Migration program sets the 5000 data types to DINT by default, and of course, the PLC5 used INT types.

My question is this - would it be good practice just to change all the generated data types from DINT to INT? Or should I only concern myself with those where a PCE pops up?

Like I said, it's a simple program, and I'm not looking to rewrite it. Just wondering if I can prevent some future issues in this way.

Thanks,

Tim Moulder

I don't like migration tools. You think you're saving time but at the end you'll need to spend time debugging the final application and rewriting logic.

Speaking about ControlLogix, using DINTs is a good practice.

TimothyMoulder said:

My question is this - would it be good practice just to change all the generated data types from DINT to INT? Or should I only concern myself with those where a PCE pops up?

Click to expand...

Tim, my experience has shown me that one should stick with DINT tags in CLX with a few exceptions:
1. Block transfer data to 1771 analog modules/older PF drives/etc.
2. MSG instructions to PLC5s
3. Anything else I can't remember that uses INT tags

Logix based processors use DINT as the atomic data type. When performing any operation on an INT, it will convert the tag data from INT to DINT prior to executing the math operation and then convert back from DINT to INT. This may not be as big of a time factor with the L7 & L8 processors as it was with the original L55s, but it is unnecessary overhead.

With cases 1 & 2 above, I buffer the data so that INTs are used in the MSG instruction but DINTs are used elsewhere in the Logix program. Hope this helps.