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Datablocks with size > 65536 bytes

Created by: Robert Carlsson at: 5/4/2009 2:23 PM (11 Replies)

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5/4/2009 2:23 PM	Rate (0)
Robert Carlsson Posts: 20 Rating: (0)	Hello everybody! I'm writing two separate function blocks that will download and upload data. There are 128 different variables with data to be uploaded/downloaded with a maximum length of 128kbyte in total. I'm writing one function block that will upload this data from a PROFIBUS slave to a PLC and store the data in the PLC. The other function block is to download this data to the PROFIBUS slave from the PLC. How can I accomplish this the easiest way? I tried to declare 4 32kbyte chunks of data in the STAT section of the header of the function block, and keep track of what data belongs to what variable with another set of variables, but this failed as the data block couldn't be bigger than 65536 bytes. The easiest way would be to declare data blocks dynamically, is this possible? I can't declare anything static though, because these blocks will be used by other users, not just in a single program written by myself. Thanks in advance
Robert Carlsson Posts: 20 Rating: (0)
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5/4/2009 8:13 PM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 3/8/2023 Posts: 703 Rating: (96)	Hello, the 64kB is the maximal length of a DBs (but it's a CPU specific, S7-315 and lesshave just 16kB). In your FB you could use an external memory for data storage (few shared DBs). It's possible to create a DBs by instructions in your block, but if you're developping it for a general use I would suggest to define the structures as UDTs and the DBs connect to your block as parameters. Regards Sydney
	Last edited by: Sydney at: 5/4/2009 8:17 PM
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5/5/2009 9:00 AM	Rate (0)
Robert Carlsson Posts: 20 Rating: (0)	Okay, I see, but how do I define this UDT? Havn't worked with these thing before...
Robert Carlsson Posts: 20 Rating: (0)
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5/5/2009 10:38 AM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 3/8/2023 Posts: 703 Rating: (96)	The UDT declaration syntax is identicalwith a datablock. In the datablock then is variable declaration of data type UDTnr. Regards Sydney

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5/5/2009 10:42 AM	Rate (0)
Robert Carlsson Posts: 20 Rating: (0)	Okay, think I know how to do this now, thanks!
Robert Carlsson Posts: 20 Rating: (0)
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5/5/2009 10:50 AM	Rate (0)
H-H Platinum Member Joined: 7/2/2008 Last visit: 3/14/2023 Posts: 928 Rating: (303)	I hope you will find this FAQ useful beside what Sydney had said.

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This contribution was helpful to 1 thankful Users Sydney

5/5/2009 4:25 PM	Rate (0)
Robert Carlsson Posts: 20 Rating: (0)	It seems taking a few DBs as input is the best way to solve this problem. The question is now; is it possible to dynamically create arrays within the DBs passed as input parameters to the FB? Since the size of each parameter is variable, the only limit is the 128k total for all parameters, it would be great to be able to create one array of Byte for each node (a total of 128 nodes). Is this possible?
Robert Carlsson Posts: 20 Rating: (0)
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5/5/2009 6:17 PM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 3/8/2023 Posts: 703 Rating: (96)	It's not allowed to create anything in existing DB, you create a wholeDB with the specified length and then it can be filled with the data. Btw are you sure that it's 128 kilobytes, not only bytes? For PB slave it's pretty much, normally it's up to 240 bytes, unless you're usingfor example S7 connectionbetween PLCs with communication... Regards Sydney

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5/6/2009 8:27 AM	Rate (0)
Robert Carlsson Posts: 20 Rating: (0)	Yes, I'm sure about the 128k. If I take two DBs as in parameters, can I delete them inside the program and then recreate them, and fill them with data, is that what you suggest?
Robert Carlsson Posts: 20 Rating: (0)
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5/6/2009 10:13 AM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 3/8/2023 Posts: 703 Rating: (96)	If the DBs already exists online, you don't need them deleted and recreated, only if you'd like to change their size, but then you should take in consideration the available work memory and if you acces them somewhere from the another part of program. Regards Sydney

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