Wieland samos PRO Manual page 163

Communication principle
In EtherCAT the master sends a telegram to the first device. This extracts the data intended for it
from the data flow, inserts its response data into the telegram and sends the telegram on to the next
device. The next device processes the telegram in the same way.
If the telegram has reached the last device, this recognizes that no more devices are connected and
sends the telegram back to the master. In this way the telegram is sent via the other pair of wires
through all devices to the master (full duplex). The connection sequence and the use of full-duplex
technology means EtherCAT is a logical ring.
Ethernet Frame
DA
EtherCAT Frame
Header
EtherCAT Datagramm
Command Header
EtherCAT Datagramm
Mailbox Header
Type = CoE (CANopen over EtherCAT)
CANopen Header
CoE Header
Number
Service
0: reserved
1: Emergency message
2: SDO request
3: SDO response
4: TxPDO
DA Destination address
CRC Checksum
Components
The components of the CoE interface are listed below:
EtherCAT State Machine
The EtherCAT State Machine controls the state of the EtherCAT coupler.
Object directory
The object directory lists all parameter, diagnostic, process or other data which can be read or
described via EtherCAT. The SDO information service provides access to the object directory.
Process data
The EtherCAT data link layer is optimized for the fast transfer of process data. This determines how
the process data of the device is assigned to the EtherCAT process data and how the application on
the device is synchronized to the EtherCAT cycle.
The assignment of the process data (mapping) is done via the PDO Mapping and the SyncManager
PDO Assign objects. These describe which objects from the object directory are transferred as pro-
cess data with EtherCAT. The SyncManager Communication objects determine the cycle time with
which the associated process data are transferred via EtherCAT and in what form it is synchronized
for transmission.
Wieland Electric GmbH | BA000970 | 07/2019 [9855]
SA Type
Datagramm Slave 01
Reserved
Data
Datagramm Slave n
...
Data Working Counter
Mailbox Service Data
CANopen Data
Service
5: RxPDO
6: Remote request of TxPDO
7: Remote request of RxPDO
8: SDO information
9...15: reserved
SA Source address
Type Ether type
(example: the entry 0x88A4 means Ether-
CAT protocol.)
EtherCAT Gateway
CRC
163