Ethercat Documentation; General; Introduction; Structure Of Ethercat® Frames - MICRO-EPSILON confocalDT IFD2410 Series Operating Instructions Manual

EtherCAT Documentation

8. EtherCAT Documentation
8.1

General

From an Ethernet point of view, EtherCAT® is an individual large Ethernet device that sends and receives Ethernet tele-
grams. An EtherCAT system like this consists of an EtherCAT master and up to 65535 EtherCAT slaves.
Master and slaves communicate via standard Ethernet cabling. On-the-fly processing hardware is used in each slave.
The incoming Ethernet frames are processed by the hardware directly. The relevant data is extracted from the frame or
inserted. The frame is then sent on to the next EtherCAT® slave device. The fully processed frame is returned from the
last slave device. Various protocols can be used at the application level. CANopen over EtherCAT technology (CoE) is
supported here. An object dictionary structure with service data objects (SDO) and process data objects (PDO) is used
to manage the data in the CANopen protocol. You can get further information from the ® Technology Group (www.ether-
cat.org) or Beckhoff GmbH, (www.beckhoff.com).
8.2

Introduction

8.2.1 Structure of EtherCAT® Frames
The data in Ethernet frames is transmitted with a special Ether type (0x88A4). An EtherCAT® frame like this consists of
one or more EtherCAT® telegrams, each of which is addressed to individual slaves / storage areas. The telegrams are
transmitted either 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 has exchanged the associated data.
Ethernet frame 0x88A4
Frame header
Destination Source EtherType
OR
IP header UDP header
Destination Source EtherType
UDP/IP 0x88A4
Fig. 74 Structure of EtherCAT® frames
8.2.2 EtherCAT® Services
In EtherCAT®, services are specified for reading and writing data in the physical memory within 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, multi-
ple writing)
- FRMW (Configured address read multiple write, reading of a physical area with fixed addressing, multiple writing)
confocalDT IFD2410/2411/2415
1. EtherCAT datagram 2. EtherCAT datagram ... Ethernet-CRC
Frame header 1. EtherCAT datagram 2. EtherCAT datagram ...
Length Resolution Type
(11 bit) (1 bit) (4 bit)
EtherCAT header Data
(10 byte) (min 32 byte)
Ethernet-CRC
Working counter
(2 byte)
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