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Powertag Indexing

Created by: conradl at: 12/9/2010 9:12 AM (5 Replies)

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12/9/2010 9:12 AM	Rate (0)
conradl Posts: 3 Rating: (0)	Hi, I have a tag that is accessed in the PLC. This tag is linked to the PLC via an index tag. The value in the tag is an address/offset of the start of our required object data. I jump to the offset that I retrieved from the tag. The object data is accessed via a powertag which uses the offset as the index (iIndex). What I want to do is then iterate through the object data by changing (iIndex) inside the script? The tags have been set up to do continuous cyclic update, 100ms. Is this possible at all or do I have to write a delay inside the iteration to wait for the update of the tag after the index has changed?
conradl Posts: 3 Rating: (0)
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12/9/2010 4:07 PM	Rate (0)
Sandman Platinum Member Joined: 4/29/2010 Last visit: 12/16/2022 Posts: 1557 Rating: (159)	Hello, do you use multiplexing in this case? best regards

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12/10/2010 7:12 AM	Rate (0)
conradl Posts: 3 Rating: (0)	Yes indeed I am. I have pasted the code below. ' Retrieve the byte offset in the DB where the object data resides ' Line\ParAddrObjDataIndex -> Index for the powertag ParAddrObjData SmartTags("Line\ParAddrObjDataIndex").Value = SmartTags("Line\ParAddrDataOffset").Value iCtr = 0 fFlag = False While (fFlag = False) ' Retrieve the object data at the ParAddrObjDataIndex iValue = SmartTags("Line\ParAddrObjData") ' Split the DWORD into two WORDs Call SplitDWORD(iValue, iObjNumber, iObjByteNumber) ' If we are at the Object with ObjNumber = 64, we hav processed all the objects in the DB If iObjNumber = 64 Then fFlag = True Else ' Move to the next Object Data in the DB by moving the index by 4 bytes ' This is where the frustration is. I dont't think I can move pointers and read the values ' during execution of the script. Is there any other way of doing this? SmartTags("line\ParAddrObjDataIndex").Value = SmartTags("line\ParAddrObjDataIndex").Value + 4 iCtr = iCtr + 1 SmartTags("iTempCtr").Value = iCtr ' Store the found object number in the internal array SmartTags("Line\iLineBinControllerNumbers")(iCtr) = iObjNumber ' Limit the number of iterations to 9 ' Not the best way of doing this If iCtr = 9 Then fFlag = True End If End If Wend
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12/10/2010 9:18 AM	Rate (0)
fbelic Silver Member Joined: 2/17/2009 Last visit: 12/1/2020 Posts: 327 Rating: (28)	Greetings Yes, if you are changing index for indexed tags, you should have a delay. Even better, don't change index of same tag more than once in function. If this was possible, you would be able to create an HMI project with only few tags Best regards

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12/10/2010 9:42 AM	Rate (0)
conradl Posts: 3 Rating: (0)	Thank you for your input. Can you give me advice on how to do this? I don't want to rely on the PLC timer functions in order to do this functionality. Regards Conrad
conradl Posts: 3 Rating: (0)
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12/10/2010 10:18 AM	Rate (0)
fbelic Silver Member Joined: 2/17/2009 Last visit: 12/1/2020 Posts: 327 Rating: (28)	Well, depends on what you are doing... If it is something that has to do with the process, do it on PLC - indexing works there very well and reliable. You could do it by calling function on "Change Value" event of 1s cycle memory bit from PLC. Just remove while iteration from your function, but leave some if condition on fFlag. Then set iCtr and fFlag somewhere outside of this function. Drawback is in the fact that this will need 9 seconds to execute. You can try using shorter cycle, but it will be more unreliable. Best regards

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