If you have set up your EtherCAT network in a daisy-chain like fashion, once you disconnect or power off a SubDevice, the remaining ones in-line go offline. This article describes how to remedy this issue.
APPLICABLE PRODUCTS
All products with an EtherCAT SubDevice interface
QUESTION
How to mitigate daisy-chained EtherCAT SubDevices going offline downstream a disconnected SubDevice?
ANSWER
EtherCAT can address up to the theoretical limit of 65535 slaves, regardless of the topology, with no impact on performance. So you could connect that many devices in a line topology.
However, once you power-off or disconnect a single one, the remaining downstream devices will no longer be reached by the EtherCAT MainDevice. Therefore, you should shift over to using a ring topology, i.e. closing the ring by connecting the last SubDevice with a 2nd Ethernet port of the MainDevice.
Alternatively, if you require SubDevices or groups of SubDevices to be powered off or disconnected independently of the rest of the network, you should consider a star topology.
REFERENCES
EtherCAT Installation Guideline, Document ETG.1600, (Guideline for Planning, Assembling and Commissioning of EtherCAT Networks)EtherCAT Compendium