Ethernet protocol, EtherCAT, processes on the fly

EtherCAT processes Ethernet frames on the fly and maps through a Fieldbus Memory Management Unit (FMMU), distinguishing it from other industrial Ethernet protocols. One EtherCAT frame holds the data for many network devices, then...


Industrial Ethernet protocols typically require individual Ethernet frames for each device on the network. Because of the Ethernet frame’s minimum length requirements as defined by IEEE 802.3, small payloads of a few bytes of data per node (typical for automation devices) results in poor bandwidth utilization. This means much of the communication is spent on overhead for the Ethernet packet, resulting in performance comparable to traditional legacy fieldbus systems.

EtherCAT’s general operating principle of “processing on the fly” for Ethernet frames, along with mapping through a Fieldbus Memory Management Unit (FMMU), distinguishes it from other industrial Ethernet protocols. One EtherCAT frame holds data for many network devices. The frame is not received and interpreted with the process data copied at each individual device. Rather, each EtherCAT slave device reads the data specifically addressed to it from the frame and inserts data into the frame while that frame passes through the node at full speed. Also, the frame’s cyclic redundancy check (CRC) is updated to reflect the new contents of the frame.

Simple integration of traditional fieldbus devices to EtherCAT is assured, including such networks as DeviceNet, Profibus, SERCOS, CANopen, and others. All data from these networks can be transmitted in the EtherCAT frame over a standard Ethernet cable. In this way, EtherCAT users can implement a gradual migration path, if necessary, to advanced industrial Ethernet. Data from other major industrial Ethernet protocols also can be transmitted over EtherCAT, including EtherNet/IP and Profinet. Besides industrial networks, EtherCAT can transmit all Ethernet Protocols: SECS, GEM, HSMS, TCP/IP, and so on. This is useful for communicating to standard TCP/IP devices, such as barcode readers, label printers, or human machine interface (HMI) screens via the EtherCAT backbone.

Other EtherCAT advantages over fieldbus systems include:

  • Very simple master and slave implementations - A synchronization method that sets the standard for determinism in industrial networks (distributed clocks)
  • Ability to implement any topology, including redundant rings and hot connect/disconnect segments, without the need for switches or any other active infrastructure components
  • Industry leading diagnostics with exact localization of faults for a variety of fault conditions
  • Lower costs than other industrial networks due to less expensive slave implementations, no infrastructure requirements, and no special master cards required.

- Joey Stubbs, PE, PMP, is North American representative, EtherCAT Technology Group. Edited by Mark T. Hoske, CFE Media, Control Engineering, 

Industrial Ethernet: Application Optimization - webcast
Friday, October 7, 2011 at 2 p.m. ET/1 p.m. CT/11 a.m. PT (... and archived after that for viewing.) 

No comments
Consulting-Specifying Engineer's Product of the Year (POY) contest is the premier award for new products in the HVAC, fire, electrical, and...
Consulting-Specifying Engineer magazine is dedicated to encouraging and recognizing the most talented young individuals...
The MEP Giants program lists the top mechanical, electrical, plumbing, and fire protection engineering firms in the United States.
Salary survey: How much are you worth?; Dedicated outdoor air systems; Energy models and lighting
Fire, life safety in schools; Fire protection codes; Detection, suppression, and notification; 2015 Commissioning Giants; Emergency and standby power in hospitals
HVAC and building envelope: Efficient, effective systems; Designing fire sprinkler systems; Wireless controls in buildings; 2015 Product of the Year winners
Designing positive-energy buildings; Ensuring power quality; Complying with NFPA 110; Minimizing arc flash hazards
Implementing microgrids: Controlling campus power generation; Understanding cogeneration systems; Evaluating UPS system efficiency; Driving data center PUE, efficiency
Optimizing genset sizing; How the Internet of Things affects the data center; Increasing transformer efficiency; Standby vs. emergency power in mission critical facilities
As brand protection manager for Eaton’s Electrical Sector, Tom Grace oversees counterfeit awareness...
Amara Rozgus is chief editor and content manager of Consulting-Specifier Engineer magazine.
IEEE power industry experts bring their combined experience in the electrical power industry...
Michael Heinsdorf, P.E., LEED AP, CDT is an Engineering Specification Writer at ARCOM MasterSpec.