Let’s describe the Hot Connect functionality in one sentence: “You can plug in/out SubDevices in your network during operation without causing an error.”

Ok, this sentence sounds quite easy. But is the functionality and the configuration that easy? In this blog, we will set up the EC-Master and three groups of SubDevices at our desk and explore the functionalities of Hot Connect.

Figure 1: Three groups of SubDevices

Some notes to the picture above:

First SubDevice group, the Mandatory Group:

• EtherCAT coupler (Beckhoff EK1100)
• 2x EtherCAT 4-channel digital output Terminal (Beckhoff EL2004)
• 2x EtherCAT 4-channel digital input Terminal (Beckhoff EL1014)
• EtherCAT 2-channel analog output Terminal (Beckhoff EL4132)
• EtherCAT extension (Beckhoff EK1110)

Second SubDevice group, the Green Group:

• Infineon XMC4800 Relax EtherCAT Kit

Third SubDevice group, the Blue Group:

• EtherCAT coupler (Beckhoff EK1101)
• 1x EtherCAT 4-channel digital input Terminal (Beckhoff EL1014)
• 1x EtherCAT 2-channel analog output Terminal (Beckhoff EL4162)

The functionality Hot Connect is one of the various Feature packs (FP) of the EtherCAT MainDevice functionalities which is defined in the official ETG (EtherCAT Technology Group) document ETG.1500 Master Classes.

With this functionality, a preconfigured section in the network can be added or removed from the EtherCAT network. All this can be done before and even during operation of the running (hot) system. In the real world, there is often the need to operate a system even if there is no perfect match between the EtherCAT network configuration (ENI file) and the currently connected and wired SubDevices.

Therefore, this option is really a great improvement, especially when you are setting up a complex control system. If parts of the system are not available, e.g. the SubDevices are powered-off or they are disconnected, you still can go ahead with setting up the system.

In addition, you gain a maximum of flexibility in the wiring of the system. The SubDevices can be connected to different ports. As an example, if a SubDevice offers both, analogue and CAN-signals, you can freely decide which interface to use.

The Hot Connect is very strong if the system is communicating with stationary and non-stationary SubDevices. One example is a Tool Changer in an automation process. After defining a set of tool groups, each tool can be easily connected and disconnected to and from the EtherCAT network.

But the Hot Connect functionality is also very interesting in systems, which are equipped with mandatory as well as optional devices. For example, in a measurement machine, there could be optional devices like scanners, special measurement sensors and other equipment included in the system. And even if these optional devices are missing or detached, the system is still running in operational state.

Now let’s go for exercising. Based on the hardware located on our desk (see Figure 1), we want to create different groups to check and test the Hot Connect functionality.

Figure 2: Topology View of the three groups of SubDevices

Figure 2 shows the current topology with the different groups. The Mandatory Group is directly connected to the EC-Master. This group of SubDevices is part of a minimum required configuration and cannot be switched on/off. The first Hot Connect Group is the Green Group with the XMC4800 Relax EtherCAT Kit followed by the Blue Group (EtherCAT coupler with two modules).

In the Blue Group, we use the EtherCAT Coupler EK1101 with ID-Switch functionality. This functionality enables the assignment of a unique ID to a group of EtherCAT SubDevices. In our case, we manually switch to the decimal value 1403. As displayed in Figure 3, the result of the hexadecimal combination of 5x256, 7x16 and 11x1 is the decimal value 1403.

Figure 3: Creating a unique ID with the three hexadecimal ID-switches

To specify and to group the SubDevices as Hot Connect Groups, we work with the EC-Engineer. First, we need to add all SubDevices into the project explorer. This can be realized by scanning the network or by adding each SubDevice manually into the project explorer. Now, we select several SubDevices in the tree view, right-click onto this group and select “Create Group” as shown in the screenshot below (Figure 4).

Figure 4: Creating a Hot Connect Group in the EC-Engineer

In the following menu (Figure 5), you can select the checkbox of the Hot Connect Group. The parameter “Identification Value” needs to be filled out with a unique identifier.

If you scan the topology with the EC-Engineer, this parameter is already filled out. In our example, we find the value 1403 as the preconfigured value. This is exactly the value which we predefined manually with the three switches. If the SubDevices do not have any ID-Switch, we will come later to alternative ways how to fill out this parameter. After confirming the changes, we are done. Congratulations – we have created our first Hot Connect Group.

Figure 5: Activating the Hot Connect Group in the menu “Group Settings”

Another option is to detach the group. You need to know that, by default, each SubDevice can only be connected to a specific port within the network. If you use the command “Detach Group”, the SubDevice can be connected to any available free port within the topology. By right-clicking on the selected group and selecting “Detach HC (Hot Connect) Group” (see Figure 6 below), we now detached the group and reach full flexibility.

Figure 6: Detach the HC Group in the EC-Engineer

Now we do a similar procedure for the Green Group. But the XMC4800 Relax EtherCAT Kit does not have an ID-Switch. What shall we do? In general, all EtherCAT SubDevices can be members of different Hot Connect Groups, even if they don’t have an ID-Switch. If you want to create a Hot Connect Group, the first SubDevice within this group needs a unique identifier. This is necessary, because the different Groups need to be identified within the network.

As Default, after scanning the network with the EC-Engineer, all SubDevices receive an identifier which is written in the register “Station Address” of the ESC (EtherCAT SubDevice Controller). To enable the Hot Connect functionality, we need to edit the register entry “Configured Station Alias”. Therefore, we need to switch the EC-Engineer to diagnosis mode and change the EEPROM values of the SubDevice. Select the SubDevice and go to the menu “EEPROM”. In the register 0x0004, we can enter a unique identifier, called “Configured Station Alias”. Select the row, enter the value and “write” to the EEPROM (Figure 7).

To finish this procedure, the identifier needs to be written into the ESC (EtherCAT SubDevice Controller) register. Therefore, we need to power off the SubDevice and restart the system.

Figure 7: Detach the HC Group in the EC-Engineer

As a result, we now created a flexible system where we can connect/disconnect our groups in any possible topology. The screenshot Figure 8 below shows the topology view of the system with the two Hot Connect Groups. Last but not least, let’s create the ENI File.

Figure 8: Topology view with the two Hot Connect Groups in the EC-Engineer

As mentioned above, most SubDevices support the Hot Connect functionality. As this feature is defined as a Feature Pack according the official ETG (EtherCAT Technology Group), an additional license for EC-Master is necessary to allow the MainDevice to handle the Hot Connect functionality.

The acontis EC-Master SDK (Software Development Kit) supports the Hot Connect functionality in a perfect way. Documentation, source code, example applications and much more will help you to create your own application. With the callback functions (Notifications), the application immediately gets feedback if there are any topology changes in the network.

In this regard, we may also want to point out to the functionality “Border Close”. There may be requirements, that the SubDevices shall connect only to specific ports. For example, in a tooling machine, the different Hot Connect Groups shall connect only to one port to avoid bus disturbance. Then, the EC-Master can close all ports which are not connected to the Hot Connect Group SubDevices.

Now let’s show how the system works in operation. After starting the EcMasterDemo on Windows with the command below (Snippet 1), the application will communicate with the Windows driver NDIS (Network Driver Interface Specification). The application will parse the ENI file and check if the option Hot Connect is active for the current system.

./EcMasterDemo -ndis 192.168.1.7 1 -f eni.xml -v 4

Snippet 1 Starting EC-Master Demo

Figure 8: EC-Master Demo detects Hot Connect Groups

After starting the EC-Master, the application detects all Hot Connect Groups and changes state into operational (Figure 8).

After starting the EC-Master, we now can look into different scenarios of the Hot Connect functionality. As we have three groups of SubDevices on our desk, we first start the system only with the Mandatory Group, meaning Green Group and Blue Group are disconnected (Figure 9).

Figure 9: EC-Master Demo detects only the mandatory SubDevices

Now we connect our first SubDevice (XMC4800 Relax Kit), defined as Green Group. As Default, the master is running in automatic mode, meaning that the EC-Master detects this modification and automatically sets the SubDevices into operational state. Now, in total 10 SubDevices are found in the network and they work in OP mode (Figure 10).

Figure 10: EC-Master Demo detects 10 SubDevices after connecting the Green Group

Next challenge for the system: Disconnecting SubDevices. We disconnect again this group and we come back to our initial configuration with our 9 mandatory SubDevices (Figure 11).

Figure 11: EC-Master Demo detects 9 SubDevices after disconnecting the Green Group

For a further test, we now connect a SubDevice, which is not configured in the ENI file. If we connect this SubDevice, we got following result (Figure 12):

Figure 12: EC-Master Demo detects unknown SubDevice

EC-Master sets a notification “EC_NOTIFY_SB_MISMATCH” which tells the application that some SubDevices are not known or wrong configured in the EtherCAT network.

Now, let’s skip the middle group for a test. We now connect the Blue Group directly with the Mandatory Group.

Figure 13: EC-Master Demo detects SubDevices from Mandatory Group and the Blue Group

The EC-Master now detects all SubDevices from the Mandatory Group and Blue Group. The Green Group was “bridged” and the corresponding SubDevices are not included in the network (Figure 13).

As a last scenario, we want to change the order sequence of the SubDevices. We mix up the topology, starting from the Mandatory Group moving on to the Blue Group and finally to the Green Group. For this scenario, we need the functionality “Detach Hot Connect Group”, which we described already in this blog. If we don’t select this option, the scenario will not be successful. To illustrate the different topologies, please check Figure 14 below.

Figure 14: Original topology and new topology after reconnecting the different groups

As a result, we see that all groups were identified. The thirteen SubDevices and the topology change was detected and the EC-Master is operational (Figure 15).

Figure 15: EC-Master detects the new topology