MICRO-EPSILON optoNCDT 2300 - A 7 Ethercat; A 7.1 Generall; A 7.2 Preamble; A 7.2.1 Structure of Ethercat-Frames

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Appendix| EtherCAT
optoNCDT 2300
A 7 EtherCAT
A 7.1 Generall
EtherCAT® is, from the Ethernet viewpoint, a single, large Ethernet station that transmits and receives Ethernet telegrams. Such an
EtherCAT system consists of an EtherCAT master and up to 65535 EtherCAT slaves. The fast transmission of the measurements is an
essential task of the EtherCAT interface.
Master and slaves communicate via a standard Ethernet wiring. On-the-fly processing hardware is used in each slave. The incoming
Ethernet frames are directly processed by the hardware. Relevant data are extracted or added from the frame. The frame is sub-
sequently forwarded to the next EtherCAT® slave device. The completely processed frame is sent back from the last slave device.
Various protocols can be used in the application level. CANopen over EtherCAT technology (CoE) is supported here. In the CANopen
protocol, an object tree with Service Data Objects (SDO) and Process Data Objects (PDO) is used to manage the data.
Further information can be obtained from ® Technology Group (www.ethercat.org) or Beckhoff GmbH,
(www.beckhoff.com). MICRO-EPSILON Optronic has the Vendor ID 0x00000607 of the EtherCAT® Technology Group.
A 7.2 Preamble
A 7.2.1 Structure of EtherCAT®-Frames
The transfer of data occurs in Ethernet frames with a special Ether type (0x88A4). Such an EtherCAT® frame consists of one or
several EtherCAT® telegrams, each of which is addressed to individual slaves / storage areas. The telegrams are either transmitted
directly in the data area of the Ethernet frame or in the data area of the UDP datagram. An EtherCAT® telegram consists of an Ether-
CAT® header, the data area and the work counter (WC). The work counter is incremented by each addressed EtherCAT® slave that
exchanged the corresponding data.
Ethernet frame 0x88A4
ODER
UDP/IP 0x88A4
Destination Source EtherType
Destination Source EtherType
1. EtherCAT datagram 2. EtherCAT datagram ... Ethernet-CRCFrame header
1. EtherCAT datagram 2. EtherCAT datagram
...
EtherCAT header
(10 byte)
Data
(min 32 byte)
Working counter
(2 byte)
Length
(11 bit)
Resolution
(1 bit)
Type
(4 bit)
Ethernet-CRC
Frame header
IP header UDP header
Fig. 62 Setup of EtherCAT frames