Scenario

When using Ethernet/IP communications between PLCs and other devices, where the PLCs have been configured using Sysmac Studio, you have encountered a ‘Tag Data Link Error’, and your communications are failing.

You may even be experiencing ‘chasing’ behaviour, where you resolve one node's error by resetting it, but then the error reoccurs in additional nodes.

Issue

The issue at hand is likely to be due to connection resources not being sufficient, which explains the ‘chasing’ behaviour of the error, as resetting a node temporarily reduces the usage of those resources before overloading them again.

This is typically due to using too many Tags or Tag Sets for the connection.

Solution

Resolving the underlying issue with the Tags or Tag Sets will require reconfiguring the Ethernet/IP settings on all of the devices using the problematic connections. If there are multiple connections, it is important to diagnose which of them are causing the issue.

We do this by navigating to the Ethernet/IP Device List in Sysmac Studio, as shown below:

Clicking on this Tool will open the following window in Sysmac Studio's main view, with the details depending on the connected PLC:

Double-click on the connected port. This opens the Built-In Ethernet/IP Port Settings window, as shown below:

In this window, we click on the button on the lower left to view the connections, as shown:

This will list all of the existing connections between the PLC on which the Ethernet/IP port is present, and the other devices on the network. On this page we can also see how many connections are present, and the maximum number that are allowed. Depending on your network infrastructure and other environmental considerations, the issue previously described can occur without the number of connections reaching the maximum.

If the maximum is exceeded, Sysmac Studio will display an error on this page.

If the issue is occurring without reaching the maximum, it's likely that we need to optimise the connections.

In the list of the connections, the IP address of each connected device is presented under the ‘Target Device’ header. Check through this list for the same IP address, and note down when this occurs, as well as the names of the Tag Sets under the ‘Target Variable’ and ‘Originator Variable’ headers.

Click back to the Tag Sets section of the Built-In Ethernet Port Settings window, using the button on the top left of the window.

In this window, look for the Tag Sets that were used in the connections with the same IP address. Expand them to view the Tags in these Tag Sets, if they were not already visible. You should see a similar table to the below image:

From here, we can see that there are two Tag Sets and two Tags, with one Tag per Tag Set. We are also going to assume that these Tag Sets are being used in two different connections to the same device.

To optimise this, we will consolidate the Tag Sets, such that the two Tags are in a single Tag Set, meaning that we only need one connection to the device.

To do this for this example, click and drag the Tag named ‘Tag2’ such that your mouse pointer is on the Tag named ‘Tag1’. Release the mouse button, and ‘Tag2’ will be moved from ‘TagSet2’ and placed beneath ‘Tag1’ in ‘TagSet1’. We can now delete ‘TagSet2’, resulting in our window looking like:

Note that the number of Tag Sets in use has reduced to one.

If we click back to our Connections page (using the button on the lower left of the current window), we may see that some of our connections have pink ‘error’ highlights, due to now-missing Tag Sets. These connections should be deleted.

Transfer these new settings to the controller to finish this process on the current PLC. Note that this process may need to be repeated on the other PLCs and devices on the Ethernet/IP network, such that they all have matching Tag Set and Tag data.

Optimisation of Tag Sets is achieved when we have a single connection between the PLC and the other device. Unless recommended by the manufacturer of the other device, it is advisable to avoid multiple connections between two devices on a network.