While I am experienced with PLCs, I have encountered a new issue. In the ladder logic, one of my indirectly addressed tags is displaying as a "??" However, when I check the tag in the Program Tags tab, the correct data is shown. Despite my attempts to overwrite the data in the ladder logic viewer, the "??" persists. Has anyone else experienced this issue and what steps should I take to resolve it? Any assistance would be greatly appreciated.
While an example would be beneficial, I will attempt to explain without one. When programming multiple TON instances with an array of TON tags and a variable index, the preset and accumulator may display as ??. This is due to the lack of a single correct value for the instruction, as multiple values exist within the array of TON tags. If this explanation does not help, can you offer an example to clarify the issue further?
Similar to this scenario, it is surprising but effective that the data type being used is a string.
Have you tried reinitializing the "ProductIDPointerValue" variable? It's possible that it is being assigned a value corresponding to an invalid element in the "PCData" array. However, it may then be updated to a valid number before the condition is met and the inequality comparison is made. Subsequently, it could be reverted back to an invalid number, causing the output to always display as '??'. This is just my hypothesis.
Despite initial doubts, the approach turned out to be effective and the process ran smoothly. To improve efficiency, I made adjustments to the logic by eliminating the indirect address and simply utilizing the tag "ProductIDPointerValue" in the comparison, along with another DINT. My aim was not to hijack the conversation, but rather to offer insight into the issue at hand for the benefit of others who may be experiencing a similar problem.
Has anyone encountered or found a solution to this issue with their PLC? After flashing my PLC, it started behaving oddly, frequently entering major fault mode. I had to make adjustments to the non-volatile memory parameters to prevent this from happening. While some values are fine, others, such as the array values like alarmstimers.[1].Pre, only show ?? instead of the expected 4000ms. This abnormal behavior is puzzling and needs to be addressed.
I've encountered this issue before. It might have to do with the scope of your tags. The ladder logic might not be able to find the tag if it is local to another program, hence showing "??" instead of the actual value. Sometimes, recompiling the program or restarting the software might fix the problem as well. If these options don't work, try to check if there are any errors in your code, paying particular attention to whether the scope of the tag in question is appropriate for its usage.
It honestly sounds like your PLC software might be experiencing some sort of glitch. Here's something you could try: re-download your PLC program to your PLC. If that doesn't work, consider creating a new dummy project, adding a similar indirect tag and observing if the problem replicates. If all else fails, it's possible that there may be an issue with the PLC software itself and you may need to update or bug report. It seems you've already tried troubleshooting the most immediate possibilities, so I hope one of these suggestions helps!
I've encountered a similar issue in the past. It may be due to the tag being used in a locked or protected routine that you can't edit without the proper permissions. Additionally, check to see if the tag is being used elsewhere in the program which might be causing a conflict. One last thought - make sure the data type of your indirectly addressed tag matches what's expected in the ladder logic; this is a common oversight which can lead to this issue.
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Answer: Answer: The display of "??" for an indirectly addressed tag in RSLogix 5000 indicates that the data for that tag is not being properly resolved or displayed in the ladder logic viewer.
Answer: Answer: To resolve this issue, you may need to check the data integrity of the tag, ensure proper addressing and referencing in the ladder logic, and potentially troubleshoot any communication or configuration issues that could be causing the problem.
Answer: Answer: If you are facing this issue, you can try overwriting the data in the ladder logic viewer, verifying the addressing and references in the ladder logic, and seeking assistance from other experienced PLC users who may have encountered and resolved similar problems.
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