BECKHOFF EtherCAT Technology Section I - Manual (Page 25)

EtherCAT Protocol
Slave Controller – Technology I-5
2.2 EtherCAT Datagram
Figure 3 shows the structure of an EtherCAT frame.
Datagram Header
FCS
FCS
Data
4 Byte
Position Addressing
1...n Datagrams
44*-1498 Byte
Ethernet header
Ethernet header
Length Res. Type
11 bit 1 bit 4 bit 14 Byte
1
st
EtherCAT Datagram 2
nd
... n
th
EtherCAT Datagram ...
Working Counter
(WKC)
Cmd Idx
Position Offset
Address Offset
Logical Address
Address Len R C M IRQ
10 Byte 0-1486 Byte 2 Byte
8 Bit 8 Bit 32 Bit 11 Bit 16 Bit 3 Bit 1 1
16 Bit 16 Bit
Node Addressing
Logical Addressing
* add 1-32 padding bytes if Ethernet frame is shorter than
64 Bytes (Ethernet Header+Ethernet Data+FCS)
Ethernet Data
EtherCAT header
16 8 62 48 59 0 63 64 79
More EtherCAT Datagrams
Figure 3: EtherCAT Datagram