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EtherCAT Bus

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General

EtherCAT is an Ethernet based field bus. The disclosed protocol is suitable for hard as soft real time requirements in the automation engineering.

EtherCAT can support almost any physical topology such as line, tree or star, and combinations of those.

The EtherCAT protocol is transported directly within the standard IEEE 802.3 Ethernet frame using Ethertype 0x88a4. It may consist of several sub - datagrams. The data sequence is independent of the physical order of the nodes in the network; addressing can be in any order. Broadcast, multicast and communication between slaves are possible.

The EtherCAT slave devices take the data dedicated for themselves while the telegram is passing through the device. Input data as well are inserted into the telegram during the cycle. A frame will not receive completely before it is processed but the processing is started as early as possible.

With gateways existing nets like CANopen, DeviceNet and PROFIBUS can be integrated into the EtherCAT environment smoothly and offer a migration path from the classic field bus to EtherCAT.

Synchronization

For synchronization a distributed clock mechanism is applied, which is equivalent to the IEEE 1588 Precision Time Protocol standard. The main clock is located in the Slave device, so there is no necessary hardware in the master. Synchronization exactness is clearly below 1µs (about 20ns with 300 nodes and more than 100m cable length).

Performance

All process data communication is handled in the slave controller hardware.The bandwidth busage is maximized since not for every participant and every datum always a single frame is needed.

Diagnostics

Bit errors in the transmission are recognized by the evaluation of the CRC hash totally reliable. The automatic evaluation of the error counters ensures the exact localization of critical network sections.

Device profiles and (Mailbox-) protocols

The device profiles describe the application parameters and the function-related behavior of the devices including the device class specific status machines. EtherCAT can provide the same communication mechanisms as they are known from the CANopen standard EN 50325-4. Kollmorgen offers the CoE (CAN over EtherCAT) profile with all important servo amplifiers. With S700 Drive motion task functionality can be controlled via the bus, too EtherCAT Motion Tasks.

User organization: EtherCAT Technology Group

EtherCAT Technology Group was founded in 2003 and is one of the greatest Industrial Ethernet user organizations today worldwide. The conformance test tool  developed with the aid of ETG members guarantees the interoperability and protocol conformity of the EtherCAT devices. Kollmorgen is a member of this group

International standardization

Since 2005 EtherCAT is an IEC standard. EtherCAT Technology Group is an official standardization partner of the IEC working groups for a digital communication. Since September 2007, moreover, EtherCAT has been SEMI standard: the E54.20 describes use of the technology in semiconductor and flat display production application.