The EtherCAT Technology Group (ETG) surprised everyone at the recent Hannover Messe by announcing that Toyota is standardizing on EtherCAT. That is a huge coup for ETG. Having one of the top automotive companies in the world select their technology, after a thorough analysis of all the industrial networks, is really big news.
So what exactly is EtherCAT?
EtherCAT is a highly speed Ethernet network that uses something called “processing on the fly.” EtherCAT messages are passed to the next node in the ring before being processed by that node, providing the network with blazing speed and efficiency. It also means that EtherCAT can offer flexibility in topology, and incredible synchronization.
Like competitive offerings, it’s a complete solution. EtherCAT includes, among other things, a safety protocol and multiple device profiles. EtherCAT also benefits from a strong user group. It offers a strong combination of benefits, and it’s why Toyota is moving to EtherCAT.
The fundamental principle of EtherCAT is that messages are not destined for a single node and consumed by that node. Instead, messages are transmitted to the following node in a string of nodes as they are processed. Input data to a node is read as the message is processed and output data is inserted in the message to the next node.
A single message is issued by the EtherCAT Master with data for all nodes. As the message is transmitted around the ring and back toward the Master, each node reads its inputs and adds its outputs to the message. When the message arrives back at the EtherCAT Master, every node in the network has received new input data from the Master and returned new output data to the Master. Without the deficiencies of small payloads or messages targeted to specific nodes, an EtherCAT network can achieve maximum bandwidth utilization.
External switches are not required in an EtherCAT network. Instead, each EtherCAT device embeds a switch. Each device has two RJ45 ports. One RJ45 is connected to the previous node in the network and one is connected to the next node.
Somewhat unique to Ethernet is the EtherCAT concept of self-terminating networks. Any node that does not detect a next node in the string automatically terminates the network at that point. Terminating nodes copy messages from the Master’s transmit path to the Master’s receive path.
EtherCAT networks can be wired in a ring if the Master has two Ethernet ports. Networks wired in a ring provide a measure of redundancy. Cable breaks anywhere in the ring are closed by the ports upstream and downstream of the break. The Master can detect the break and send messages out to both of the new sub-segments. Because of this self-terminating feature, EtherCAT networks can be wired using several different topologies including star, line, or tree.
Synchronization is another advantage of EtherCAT systems. EtherCAT includes a distributed clock mechanism, giving it a low jitter that meets the specifications of IEEE 1588 without additional hardware. The mechanism is possible because of the timestamps each node includes in the EtherCAT frame.
Each node attaches a timestamp to the EtherCAT frame twice. First, the slave node adds a timestamp when receiving the message as it is sent through the network; then, when the frame returns back through the nodes, each slave adds another timestamp. The Master receives the frame with two timestamps per slave.
EtherCAT is a very high performance, easy to deploy, open application layer protocol for Ethernet applications. Its synchronization capabilities and full bandwidth utilization are very attractive for motion applications where synchronizing large numbers of drives is required. It saves installation expense by eliminating the need for most switches, routers, and hubs.
EtherCAT fits well in the spectrum of Ethernet application layers where performance, topology, and overall deployment cost are driving factors.