Beckhoff CU2508 - Start; Fig. 18 Use of the CU2508 as an Ethercat Real-Time Environment; Fig. 19 Message Relating to CU2508 Fifo Sizes

Product overview
Real-time Ethernet port multiplier22
Version: 2.6
Fig.18: Use of the CU2508 as an EtherCAT real-time environment
There are currently still restrictions (TwinCAT 2.11/3.1, FW10) with regard to
• external synchronization of the CU2508
The influence on the internal CU2508 clock is still in preparation.
• Profinet [
}46]
• BACNet
• time stamp-controlled sending/receiving of frames
The implementation of these and further protocols is in preparation.
Data traffic in the lower-level EtherCAT segments
From FW07 and ESI revision -0018, Ports 1 and 5 have a larger data buffer of 16 kbyte (instead of 8 kbyte)
for EtherCAT segments with particularly high data transfer rates.
"High data traffic" is generated by IO systems with many cyclical data, e.g. when many subscribers (over
100) and/or subscribers with large data requirements (e.g. analog oversampling terminals) are used.
If a "large" IO system is operated in EtherCAT redundancy mode, it is advisable to use ports 1 and 5.
The memory situation found is occasionally reported by TwinCAT with "Cu2508 fifo sizes...":
Fig.19: Message relating to CU2508 fifo sizes
2.4 Start
For commissioning
• install the CU2508 as described in the Mounting and wiring [
}23] chapter
• configure the CU2508 in TwinCAT as described in the Commissioning [
}29] chapter
Furthermore, the field devices typical for the application are required on the downlink ports.