SIMATIC WinCC Open Architecture Forum

Hello,

We have configured a modbus driver to communicate with a PLC. In each address the option 'Old/New Camparison' has been checked.

We have subscribed to some points with a dpConnect to generate an XML file. We noticed that the dpConnect was called on the change of timestamp of the variable while the value of the information did not change.

Do you know how the timestamp could have changed without changing the value?

Thanks in advance.

The address option 'Old/New Comparison' only has an effect on the values written by the driver. Besides the value it also looks at the statusbits for example the invalid bit is written without a value change.

So reasons why the timestamp changes without a value change are: the same value can be written by another manager or the statusbit/userbits have changed.

You can can include the '_value_changed' and/or '_manager' in your dpConnect to determine which callbacks are relevant. With the config entry 'ignoreManager' it is possible to ignore all value changes from a specific manager.