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DB UNLINK

Created by: veer at: 6/6/2011 12:07 PM (7 Replies)

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6/6/2011 12:07 PM	Rate (0)
veer Posts: 103 Rating: (0)	HI EVERYONE what is the benefit to unlink the db and how it is possible thanks
veer Posts: 103 Rating: (0)
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6/6/2011 12:12 PM	Rate (0)
Niranjan Prasad Posts: 691 Rating: (37)	May be this thread will help you https://www.automation.siemens.com/tf/WW/en/Posts/45535
Niranjan Prasad Posts: 691 Rating: (37)
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6/6/2011 5:30 PM	Rate (0)
Aret Posts: 2348 Rating: (265)	To mark block as unlinked - right click on block, properties - find a "unlinked" check-box there. Alternatively use "Unlinked" in STL/SCL source (if you generate DB through them). On how it works - see Daniel's explanations in a link, provided by Shar. Please also mention, that you can't create all DBs simultaneously in PLC - you should create few, work with them, then delete - and this exhausts MMC resources on read/write cycles. Could you please post the whole task here - maybe there are another ways to solve your issue.
Aret Posts: 2348 Rating: (265)
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6/7/2011 6:05 AM	Rate (0)
Saravana kumar Platinum Member Joined: 2/6/2009 Last visit: 1/6/2026 Posts: 940 Rating: (119)	veer HI EVERYONE what is the benefit to unlink the db and how it is possible thanks Hi, Unlink DB is to unlink the data block from the Work Memory of the CPU. So that that DB will be only loaded into CPU and that is called as load memory. You can call that DB in the logicby using SFC 83 (READ_DBL)to connect it into the Workmemory and you can write the data by using SFC 84 (Write_DBL). This is very useful when you go for a project with more complecated logic with lower end CPU which has less work memory. I have used this in my project. The sample program is available in the forum. You can find th elink in Shar's thread.
	Last edited by: Saravana kumar at: 6/7/2011 7:33 AM Last edited by: Saravana kumar at: 6/7/2011 6:11 AM Last edited by: Saravana kumar at: 6/7/2011 6:07 AM _______________________________________________________________ Best Regards T.Saravana Kumar "All for the Best"
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6/7/2011 7:09 AM	Rate (0)
Amit_86 Posts: 1750 Rating: (272)	Saravana kumar veer HI EVERYONE what is the benefit to unlink the db and how it is possible thanks You can call the DB in the logicby using SFC 83 (READ_DBL)to connect it into the Workmemory and you can write the data by using SFC 84 (Write_DBL). Little addition Depending on the CPU, the contents of DB canbe transferred to the working memory by using SFC20 BLKMOV or SFC83 READ_DBL.
Amit_86 Posts: 1750 Rating: (272)
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6/7/2011 7:30 AM	Rate (0)
Saravana kumar Platinum Member Joined: 2/6/2009 Last visit: 1/6/2026 Posts: 940 Rating: (119)	Amit_86 Saravana kumar veer HI EVERYONE what is the benefit to unlink the db and how it is possible thanks You can call the DB in the logicby using SFC 83 (READ_DBL)to connect it into the Workmemory and you can write the data by using SFC 84 (Write_DBL). Little addition Depending on the CPU, the contents of DB canbe transferred to the working memory by using SFC20 BLKMOV or SFC83 READ_DBL. Hi Amit, I don't think that you can directly use SFC 20 to copy the contents of the DB which is located in the load memory of the CPU ( DB with unlink enabled) to workmemory. We should use the SFC 83 only. The SFC 20 can be used to exchange the data's between the DB's in the work memory of the CPU.
	Last edited by: Saravana kumar at: 6/7/2011 7:31 AM _______________________________________________________________ Best Regards T.Saravana Kumar "All for the Best"
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6/7/2011 8:22 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 1/18/2026 Posts: 3054 Rating: (1062)	Saravana kumar I don't think that you can directly use SFC 20 to copy the contents of the DB which is located in the load memory of the CPU ( DB with unlink enabled) to workmemory. We should use the SFC 83 only. Both can be used (SFC20 OR SFC83)and apart from the link thatdchartier listedin the threadthat Sharrefered too, the following may prove useful too: How can the program runtime be optimized if the main memory of the CPU is too small for the runtime-relevant STEP 7 program?"
	Last edited by: fritz at: 6/7/2011 8:25 AM 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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6/7/2011 8:29 AM	Rate (0)
Amit_86 Posts: 1750 Rating: (272)	fritz Saravana kumar I don't think that you can directly use SFC 20 to copy the contents of the DB which is located in the load memory of the CPU ( DB with unlink enabled) to workmemory. We should use the SFC 83 only. Both can be used (SFC20 OR SFC83)and apart from the link thatdchartier listedin the threadthat Sharrefered too, the following may prove useful too: How can the program runtime be optimized if the main memory of the CPU is too small for the runtime-relevant STEP 7 program?" Dera fritz Thanks for confirming that SFC20 can be used. i got confused for a while. Now it is clear that both SFC can be used.
Amit_86 Posts: 1750 Rating: (272)
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