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Blog Comments posted by Simon
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Ooooh! Didn't know about the V570 firmware upgrade for 16-bit colour.
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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...
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Looks like I have posted twice, and can't see how to delete the second copy - HELP!
(Phil: Deleted!)
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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...
PLC Scan Time (Enhanced Family)
in Simon's Blog
A blog by Simon in General
Posted
I haven't done any relative comparison. However, the programmer who triggered this post has generously provided the following feedback:
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.