Hello

I'm currently working on improving the programming for a hydraulic press system. In the existing code (TIA Portal), there are five tags that indicate the system is in Automatic Operation when all of them are non-zero.

What’s puzzling is that these tags don't appear to be getting written to anywhere in the logic -aside from being reset to zero when working status is cleared. Despite this, they somehow change value during operation.

I didn’t write the original program and I'm still relatively new to working with TIA Portal, so I’m trying to reverse-engineer the cause. Could anyone help me identify what might be updating these tag values?

I have uploaded screenshots screenshots showing every instance where these tags are used in the code. 

Any guidance or suggestions would be really appreciated.

Thanks!

There can be indirect access to the emory area, that you can't find with cross reference. Also they can be modified from the HMI.

Since you haven't created the original program, you need to go through the whole program to see if there's a indirect access to those memory areas somewhere.

The tags don't modify by them self.

Thank you Hati and Qwazee, both your suggestion help.