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Appendix |EtherCAT Documentation
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A 6
EtherCAT Documentation
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.
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 subse-
quently 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 pro-
tocol, 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).
A 6.1
Preamble
A 6.1.1 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 EtherCAT® 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-CRC
Frame 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. 82 Setup of EtherCAT frames
A 6.1.2 EtherCAT® Services
In EtherCAT® services for the reading and writing of data are specified in the physical
memory of the slave hardware. The following EtherCAT® services are supported by the
slave hardware:
-
APRD (Autoincrement physical read, Reading of a physical area with auto-increment
addressing)
-
APWR (Autoincrement physical write, Writing of a physical area with auto-increment
addressing)
-
APRW (Autoincrement physical read write, Reading and writing of a physical area with
auto-increment addressing)
-
FPRD (Configured address read, Reading of a physical area with fixed addressing)
-
FPWR (Configured address write, Writing of a physical area with fixed addressing)
-
FPRW (Configured address read write, Reading and writing of a physical area with
fixed addressing)
-
BRD (Broadcast Read, Broadcast Reading of a physical area for all slaves)
-
BWR (Broadcast Write, Broadcast Writing of a physical area for all slaves)
-
LRD (Logical read, Reading of a logical storage area)
-
LWR (Logical write, Writing of a logical storage area)
-
LRW (Logical read write, Reading and writing of a logical storage area)
-
ARMW (Auto increment physical read multiple write, Reading of a physical area with
auto-increment addressing, multiple writing)
-
FRMW (Configured address read multiple write, Reading of a physical area with fixed
addressing, multiple writing)
