EtherCAT Hot Connect is a feature that lets defined groups of slave devices be plugged in or removed while an EtherCAT network keeps running, without the whole segment faulting. Normally a break anywhere in an EtherCAT line would disrupt communication, but Hot Connect designates certain groups as optional and expected to come and go, such as a swappable tool on a machine or a removable module. The master is told these groups may appear or disappear and handles the changed topology gracefully. For modular machines and tool changers, this turns an unavoidable full-line fault into a planned, tolerated event that a monitoring layer can track.
EtherCAT Hot Connect in one line: EtherCAT Hot Connect lets predefined groups of slaves be connected or disconnected during operation without faulting the rest of the network. These Hot Connect groups are identified by fixed addresses so the master recognises them whenever they appear, and it treats their absence as expected rather than as an error, which suits tool changers and modular machine sections that are attached and removed while running.
EtherCAT works by passing a single frame down a line of slaves and back, with each slave reading and inserting its data on the fly as the frame flies past. This processing-on-the-fly design is what makes EtherCAT fast, but it also means the devices are expected to form a continuous path. If a slave in the middle of the line vanishes, the path is broken and the frame cannot complete its journey as planned, which normally shows up as a fault affecting communication beyond the break.
That behaviour is fine for a fixed installation where the set of devices never changes, but it is a problem for machines designed to be reconfigured. Consider a robot with interchangeable end-of-arm tools, each carrying its own I/O, or a production line where a whole module can be rolled in or out. If every tool change or module swap faulted the network, the machine would be unusable in the way it was intended. Something is needed to tell the master that certain parts of the topology are meant to be optional.
Hot Connect is precisely that mechanism. It lets the engineer declare specific groups of slaves as Hot Connect groups, meaning the master should expect them to be present sometimes and absent other times. Instead of treating the disappearance of such a group as a catastrophic break, the master treats it as a known, tolerated state, and it is ready to reintegrate the group cleanly when it reappears. The rest of the network carries on regardless.
For Hot Connect to work, the master has to be able to recognise a group whenever it turns up, regardless of exactly where or when it is plugged in. This is why Hot Connect groups are identified by fixed addresses rather than by their position in the line. Each group is given a stable identity, often via a configured station alias stored on the device, so that when it appears the master knows which group it is and how to slot it into the running configuration, rather than being confused by a device showing up in an unexpected place.
When a Hot Connect group is removed, the master notes that the group is now absent and continues operating with the remaining devices, keeping the segment alive. When the group is connected again, the master detects the new devices, checks their identity against the configured group, brings them through the state transitions needed to join the operational network, and resumes exchanging data with them. From the outside this looks like the group simply appearing and disappearing on demand, while the machine keeps running throughout.
This graceful handling is what enables so-called plug-and-produce behaviour on modular machines. A tool changer can swap tools mid-operation, or a machine cell can accept a different module for a different product, and the network adapts without a full restart. The master's ability to hold a place for optional groups, recognise them by their fixed identity and reintegrate them cleanly is the core of the feature, and it is what separates a genuinely modular EtherCAT machine from a fixed one that must be stopped and reconfigured for any change.
For a monitoring platform, Hot Connect introduces a topology that legitimately changes over time, and that has to be understood rather than treated as constant errors. A tool being removed is not a fault to alarm on; it is an expected event. A monitoring layer needs to distinguish an intended Hot Connect group absence from a genuine unplanned disconnection, so that operators are not flooded with alarms every time a machine does exactly what it was designed to do during a normal tool change.
The information the master already has makes this possible. Because the master knows which Hot Connect groups are configured and can report which are currently present, that presence status is a clean signal to surface upward. A cloud SCADA system can show which modules or tools are currently attached to a machine and log when they came and went, turning what would otherwise be a confusing series of appearances and disappearances into a clear, meaningful record of how the machine was configured over its shift.
For an operator running modular or reconfigurable equipment, a platform like Merobix can use that record to make the machine's changing shape legible. Trends and events can be interpreted in the light of which module was fitted at the time, so a performance change can be tied to the tool that was in use, and an unexpected group loss can be flagged as a real problem while a planned swap is logged quietly. The monitoring layer sits above the real-time EtherCAT reconfiguration, consuming the presence information rather than driving it, but it makes the modularity visible to the people who need to understand what the machine was actually doing.
The engineer declares certain slave groups as Hot Connect groups, and the master is told these may be present or absent. Instead of treating a missing group as a broken line, the master tolerates the gap, keeps the rest of the segment running, and reintegrates the group cleanly when it reappears.
Hot Connect groups are identified by fixed addresses rather than by their position in the line, often using a configured station alias stored on the device. This stable identity lets the master recognise which group has appeared and slot it into the running configuration wherever and whenever it is connected.
It is used for machines that are reconfigured during operation, such as robots with interchangeable tools or production cells with removable modules. Hot Connect lets those parts be attached and removed while the machine keeps running, enabling plug-and-produce flexibility without stopping and reconfiguring the whole network.
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