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IM151-8 PN/DP CPU - Highest address that’s allowed in function block?

Created by: AXIS at: 8/19/2011 2:21 PM (4 Replies)

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8/19/2011 2:21 PM	Rate (0)
AXIS Posts: 15 Rating: (0)	Hi, The highest address in my function block right know is 59.7. When I try to add a signal the address will be 60 and the diagnostic buffer says: Area length error when reading Instance DB, word access. Access address: 60 Where can I find information about the highest address that’s allowed in function block for this CPU? Maybe it is 59.7… I am using an IM151-8 PN/DP CPU. Best regards AXIS
AXIS Posts: 15 Rating: (0)
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8/19/2011 4:30 PM	Rate (0)
yy1 Gold Member Joined: 3/24/2009 Last visit: 1/5/2023 Posts: 535 Rating: (110)	Dear AXIS, the size of the instance-DB is defined by its FB. You can try to find out which DB is accessed. Then you can open the block and you'll see its parameters and in the 'offset'-column you see the size of the block. You also can find out the related FB and look at the interface (see attached image). In the example the size is 4 bytes (offset 2 + size for datatype INT). Hope this helps! Best regards, yy1 Attachment size_idb.jpg (34 Downloads)

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8/19/2011 7:08 PM	Rate (0)
fbelic Silver Member Joined: 2/17/2009 Last visit: 12/1/2020 Posts: 327 Rating: (28)	Greetings I had simillar problem few months ago, but with inputs and outputs. It turned out that the problem was in PLCSIM, it has some kind of restrictions. The same program worked fine on real PLC. Are you testing you program on PLCSIM or on PLC? Best regards

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8/22/2011 11:54 AM	Rate (0)
AXIS Posts: 15 Rating: (0)	Hi, If you look on the pictures of my FB and DB you see the STAT-signals with address 60 and 62. If I download this to the real PLC the diagnostic buffer will look like this: Area length error when reading Instance DB, word access. Access address: 60 If I delete those signals (address 60, 62) and download, everything looks fine. I don’t know if I can extend my FB with more signals?If not, I need to split the code into 2 FB´s and I really don’t have the time for that… /AXIS Attachment FB, DB.jpg (38 Downloads)
AXIS Posts: 15 Rating: (0)
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8/22/2011 3:18 PM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/3/2023 Posts: 2966 Rating: (1025)	Hello AXIS to start with, the latest IM151-8 PN/DP CPU (6ES7151-8AB01-0AB0) has a maximum DB size of 64 KByte (see HERE for more). This limit also applies for Instance DB's, so you have plenty of space left in your FB to declare STAT variables. If you have an olderIM151 it may be less, punch in its part number at https://support.automation.siemens.comto find it technical spec or go online in your CPU and check the performance data tab of theModuleInformation. Could it be that you perhapsnot recreated the FB's Instance DB or that you did not download it? (it's the only explanation I have for your problem). I hope thishelps
	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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