[PLC Scan Time (Enhanced Family)]

I haven't done any relative comparison. However, the programmer who triggered this post has generously provided the following feedback:

I found the amount of variables on the screen greatly effects the scan time, the page I was operating with a large amount of variables was making the cycle scan time slow to 4mS & when I changed screens (to one with only 4 variables) the scan time dropped to 1mS with no change to the plc code.

This means that I can achieve my customers requested scan time of 1mS by just changing screens at the appropriate time with no issues.

So the screen does affect scan time, but this suggests it relates more to the number of variables rather than the size of the screen. 4ms still looks pretty good for any general purpose PLC task.

[Great new products on the way...]

Ooooh! Didn't know about the V570 firmware upgrade for 16-bit colour.

[Feelin' a little Loopy!]

Thanks Ash (and Phil), that's good to know, I will make more use of it. In this case I am glad my initial assumptions were wrong!

Nothing like an endless loop to really foul things up...

[Feelin' a little Loopy!]

Looks like I have posted twice, and can't see how to delete the second copy - HELP!

(Phil: Deleted!)

[Feelin' a little Loopy!]

Hi Phil,

Thanks for the post. This is of interest to me as I have come from a background of PC-based programming and it's always a brain-stretch to cross between that and PLC ladder logic.

Whilst I generally agree with the usefulness of loops, my understanding of jumps in the Unitronics world is that they only jump forwards, not backwards. So the "jump back" actually causes the PLC to end the scan at the jump instruction and start the next scan at the jump label. So in the example of a loop, n interations would take n scans, and the other code in the program would not be executed during this time. If the code in the loop is short and the PLC is fast (like the V570) then this wil still execute reasonably well.

This isn't confirmed knowledge, and the help file is not definitive on this point. A simple program could be used to test it, or if a Unitroics engineer is reading, it could be confirmed by revelation. Or maybe I am wrong all together...