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OB35 - 100ms clock

Created by: nbk at: 10/4/2010 8:00 PM (5 Replies)

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10/4/2010 8:00 PM	Rate (0)
nbk Posts: 197 Rating: (3)	Dear all, In OB35 : AN M 0.2 = M 0.2 In OB1 :A M 0.2 R M 0.2 = M 0.4 "cyclic 100ms" I've few questions: 1. If OB1 is not programmed, what should be the status of M0.2 after 100ms or between each 100ms? 2.Why cannot we reset the bit M0.2 in any other FC? Is it being reset in OB1 because OB1 comes periodically? 3. What is the guarantee that OB1 will reset M0.2 perfectly on-timeso thatthe 100ms schedule timeand logic inOB35 is executed properly (I mean what if the CPU takes longer time to come to OB1 due to program length or size)? Regards
nbk Posts: 197 Rating: (3)
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10/4/2010 10:10 PM	Rate (0)
Zenta Silver Member Joined: 10/12/2006 Last visit: 11/15/2024 Posts: 206 Rating: (25)	nbk Dear all, In OB35 : AN M 0.2 = M 0.2 In OB1 :A M 0.2 R M 0.2 = M 0.4 "cyclic 100ms" I've few questions: 1. If OB1 is not programmed, what should be the status of M0.2 after 100ms or between each 100ms? 2.Why cannot we reset the bit M0.2 in any other FC? Is it being reset in OB1 because OB1 comes periodically? 3. What is the guarantee that OB1 will reset M0.2 perfectly on-timeso thatthe 100ms schedule timeand logic inOB35 is executed properly (I mean what if the CPU takes longer time to come to OB1 due to program length or size)? Regards wrong sequence. try ob35 set s m0.2 becouse ob1 cycle time is bigger then 100ms the ob35 run it again and the m0.2 reseted by ob35. regards Zenta

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10/5/2010 4:00 PM	Rate (0)
nbk Posts: 197 Rating: (3)	Thanks for the reply Zenta, So , In OB35 : AN M 0.2 S M 0.2 while maintaining same codes in OB1? Actually,I was looking for answers to my questions. Regards
nbk Posts: 197 Rating: (3)
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10/6/2010 2:53 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/19/2024 Posts: 3027 Rating: (1057)	nbk In OB35 : AN M 0.2 = M 0.2 In OB1 :A M 0.2 R M 0.2 = M 0.4 "cyclic 100ms" I've few questions: 1. If OB1 is not programmed, what should be the status of M0.2 after 100ms or between each 100ms? Assuming OB35 call rate is 100ms, M0.2 will be ON for 100ms, OFF for 100ms, ON for 100ms etc. etc. nbk 2.Why cannot we reset the bit M0.2 in any other FC? Is it being reset in OB1 because OB1 comes periodically? Resetting M0.2 in "any other FC" that it being called from OB1can be done, but will not change/improve the functionality of the logic. OB35 will simple toggle the status of M0.2 every time it is called (e.g. every 100ms). OB1 now (cyclically) checks it is ON and - if so - resets it and sets M0.4 ON for one (OB1) scan. It seems the aim of the logic is to create a One Shotbit (M0.4) in a rather convoluted way. They could have just used the CPU clock bits together with a rising edge detection to do so (perhaps this S7 "logic" comes from an S5 upgrade?). nbk 3. What is the guarantee that OB1 will reset M0.2 perfectly on-timeso thatthe 100ms schedule timeand logic inOB35 is executed properly (I mean what if the CPU takes longer time to come to OB1 due to program length or size)? OB1 will reset M0.2 when the logic in OB1 is executed. OB35 can and willinterrupt the cyclic (OB1 related) at any time as per its configured call rate. Once OB35 has set M0.2 ON, he reset of itis can as suchbe "delayed" by as much as OB1 scan time(e.g. OB35 interrupt to set M0.2 ON took place right after the OB1 M0.2 related reset logic was executed). As OB35'sexecution is timed by the OS in the background (i.e. independend of OB1 cycle time), you willhave on average a 100ms one shot with M0.4, as long as OB1's cycle time is less than the call rate of OB35. I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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10/6/2010 10:20 AM	Rate (0)
nbk Posts: 197 Rating: (3)	Thanks for the reply Fritz. @ Fritz : "I hope this helps" Yes , definitely it does ......... and it brings out even more info than what is available with the context-sensitive help of Simatic Manager ! @ Fritz : "....as long as OB1's cycle time is less than the call rate of OB35. " Just one thing : For what reason is it possible that OB1 will come later than 200ms ..... due to big size of program? Regards
nbk Posts: 197 Rating: (3)
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10/6/2010 10:55 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/19/2024 Posts: 3027 Rating: (1057)	nbk Just one thing : For what reason is it possible that OB1 will come later than 200ms ..... due to big size of program? Program size as wellas "runtime intensive" programming (e.g.doing search or sort loops throughlarge arrays)are the main candidates for larger cycle times. Having said that, the default cycle time monitoring setting is 150ms in a 300 CPU (which can be changed) andone must try really hard to exceed even 100ms cycle time in a modern 300 CPU in my humble oponion (it's not unheard of though).
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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