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dalucero

1747-L551C\RSLogix 500 program writing to unused address

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Does anybody know what would cause my 1747-L551C to write a value to unused float address? In my F14-Float data file, at address F14:11, something is writing the value '1562' to this address. However, when I right click on this value and select "Find all", it's not referenced anywhere in my program. David

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First, if there is an operator interface on the system, check to see if it is writing to the system. Second, it could have been used as a way to track the program to a specific machine. Does the number 1562 mean something? Like the following: Asset number? Line number? Serial number? Job number? Drawing number? If someone other than your company provided the machine, it could relate to one of their job numbers as well. We use float or string registers to on a system we have duplicated where the hardware and hmi screens are all the same. When the operators log data or print screen, the screen or logged data include the line number. Just a couple thoughts.

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And if the above does not help, post your .RSS file and maybe someone can spot something. "Find all" does not always find all.

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For example... indexed or indirect addresses...

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My guess is HMI

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I would also suggest you try cross-reference not just find-all. For example COP N17:0 F14:10 10 will write a value into F14:11 and not yet show up in a find all. BTW and BTD also can do this IIRC. You also want to look and see if any other networked PLC is writing to the address also.

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In the data table view of that address, hit the usage button. This will show you if that element is part of a file type instruction, like COPy (as long as you have cross reference enabled) . Also, do a find for "F14:[" (no quotation marks). This will help you find element level indirection that may be writing to it. Next Find "F:[" This will help locate file level indirection (less common but you never know). Edited by OkiePC

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You probably have a remote device writing to that address. Fairly common occurence. Edited by Ad Infinitum

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