BECKHOFF ET2000 - Manual (Page 16)

Product overview
Fig. 8: Configuration and transmitted EtherCAT datagrams
The EtherCAT Master (A) transmits an Ethernet frame with the process data (B) cyclically every 1 ms. This
frame contains 5 EtherCAT datagrams (C). These datagrams are automatically calculated in the TwinCAT­
EtherCAT Master. The calculation can be influenced in the 'Advanced Settings' or by SyncUnits.
The 2nd datagram, ‘LWR’, will be taken here as an example. This “Logical Write” is 1 byte long (Len = 1) and
is located in the 4.2 GB EtherCAT address space at the logical address 0x10800 (D). One or more EtherCAT
slaves must process this datagram in passing. After all slaves have done this successfully, the datagram
must come back with a WorkingCounter = 1 (E).
The entire Ethernet frame encompasses 94 bytes (F) and, in the 1 ms cycle used with a length/duration of
9.44 µs, still allows a great deal of space for further process data or acyclic/queued telegrams.
Whereas the acyclic telegrams can change during the application runtime, the cyclic telegrams in the
TwinCAT­EtherCAT Master are unchangeable as a rule. This simplifies the interpretation of the logs.
Information about the slave
We shall now consider the EL2008 slave. From its “Advanced Settings” ­­>FMMU/SM, fig. "EL2008 mapping
settings", we can see:
• that it uses only 1 FMMU (Fieldbus Memory Management Unit) (B),
• which transfers 1 byte (length = 1)
• from the logical address space at byte 0x10800 (C)
• from bit 0 (L Start: “.0”)
• to bit 7 (L EndBit = 7)
• into the Slave’s physical RAM memory after address 0x0F00 (D).
These settings are made automatically by the TwinCAT­EtherCAT Master.
The LWR at log. 0x10800 must now be sought in the telegram logs.
ET2000 16 Version 2.0