1756-L7x math/compare execution time based on tag type

[RonJohn]

I'm checking on somebody else's very first PLC5 to CLX program conversion for them and noticed most integer tags were kept as INT rather than DINT. (it was a manual conversion as the Rockwell convert tool kept crashing). I had always been taught that performing math (and maybe compare?) instructions with DINT tags was much faster than with INT tags.

I looked for a Rockwell KB document, but came up empty. Tech support basically said I was all wet when I contacted them. This old thread, especially post #5, seems to back up what I was taught though.

Has something changed with the L7x processors where it doesn't matter which data type is used any more? I want to start them off on the right path and keep me sane as well. Thanks in advance for your help.

 

[rdrast]

32 bit values (DINT / REAL) are what the CPU handles natively. Any other integer type has an implicit conversion to DINT, and wastes space. Would you notice that as a performance hit? probably not, but it is generally better to try to always use the CPU native types.