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Cyclic Program Processing order - PII PIQ

Created by: Sims at: 5/1/2012 8:06 AM (4 Replies)

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5/1/2012 8:06 AM	Rate (0)
Sims Advanced Member Joined: 5/23/2008 Last visit: 8/7/2023 Posts: 19 Rating: (0)	Hi All, Why did Siemens change the cyclic processing order from a) Operating System Tasks, Read Inputs, Process Logic, Write Outputs to b) Operating System Tasks, Write Outputs, Read Inputs, Process Logic Just curious.

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5/1/2012 10:28 AM	Rate (0)
gre_m Posts: 947 Rating: (45)	Old version work as - Read Inputs, Process Logic, Write Outputs now: Write Outputs, Read Inputs, Process Logic system task, communication work after OB1. in 400-cpu system task and communication work in 1ms slices. %time from 1ms define in Hw-config. details in documentation by step7
gre_m Posts: 947 Rating: (45)
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5/2/2012 1:07 AM	Rate (0)
Sims Advanced Member Joined: 5/23/2008 Last visit: 8/7/2023 Posts: 19 Rating: (0)	yes, but why the change in theorder? What is the benefit of changing the order?
	Last edited by: Sims at: 5/2/2012 1:07 AM
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5/3/2012 3:26 PM	Rate (0)
Aret Posts: 2348 Rating: (263)	Guess it's just to underline, that after setting outputs in OB1 some time passes before they proceed further.
Aret Posts: 2348 Rating: (263)
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5/3/2012 7:30 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (149)	I guess has something to do with jitter. If you execute program in interrupt outputs will always be set at equdistant time as well read of inputs, no matter of computing time - except is always delayed for one sample period - this could be taken into account in program. Same philosophy is in isochrone mode, so I presume they did for entire system the same thing even if in cyclic execution has no significance, but also doesn't hurt anything.

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