Updated Behavior for _Error and _NoError system tags for Modbus TCP Ethernet driver in V6.11.764.0
The documented and expected behavior for the _Error and _NoError system tags for all TOP Server drivers is that the tags' values will change state based on the "Device Not Responding" error behavior once the driver has gone through all timeouts and retries as defined in the properties for a device. This has always been the case for all TOP Server drivers. However, prior to TOP Server V6.11.764.0, the Modbus TCP Ethernet driver changed the states of those system tags based on different criteria that was not consistent with all other drivers or with the help file documentation.
Current Behavior (as documented and consistent with all other drivers)
The _Error and _NoError system tags will toggle state when the corresponding device enters an unresponsive state and the Modbus TCP Ethernet driver has gone through all configured retries and timeouts with no response. _Error will change state from False/0 to True/1 and _NoError will change state from 1/True to False/0 until the affected device starts responding again.
Previous Behavior (prior to V6.11.764.0)
The _Error and _NoError system tags would toggle state under either of the following conditions:
- When the corresponding device enters an unresponsive state and the Modbus TCP Ethernet driver has gone through all configured retries and timeouts with no response, or
- When the device responds with a Modbus Exception response due to an invalid address being requested
This could result in these system tags changing state even if other tags/addresses were still returning good values and good quality, which was misleading since the device was actually responding.