slc 5/05 scan time slowed down

Hi everyone,

we have just installed a line using a slc 5/05 cpu 32 k memory.

When we first started debugging the machine, the scan time was around 18ms. mow that the machine is running, its 40 ms and we cannot figure out why. there were (2) different guys programming the line, each had their own laptop.

i have debugged machinery hundreds / thousands of times before
when working for an oem and have never experienced this?

I am unable to post the code but there are 30-50 subroutines,
2 pid loops, analog.

any clues?

thanks in advance,
james

James Mcquade said:

I am unable to post the code

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any clues?

Click to expand...

It's going to be hard to help you since you can't post the code.

Accessing M0 and M1 files is also a big time scan hit. It's better to copy a big chunk of them to internal memory than acess individual bits and ints multiple times.

Indirect addressing adds scan time versus direct addressing.

Math functions aren't too bad unless you get into trig functions which can be a killer.

Immediate instructions are also a significant hit.

STI routines are one place where a very simple change can have a huge impact on scan time (imagine changing the STI interval from 50ms to 5ms such that it goes from running once every 3 main scans to 4 or 5 times per main scan.)

Communications can impact SLC scan time.

Having edits existing will also nail you and this one can be huge too depending on how many edit zones are installed.

There are probably other things I am not able to think of right now...