Fig. 14 Cu2508 Uplink Delay - Beckhoff CU2508 Documentation

Fig. 14: CU2508 Uplink Delay
◦ These delays are therefore relatively insignificant compared to the other factors mentioned above.
What immediately catches the eye, however, is the importance of the frame length and the
required buffering in the uplink.
CU2508 als EtherCAT slave
Each downlink port of the CU2508 can be configured as a separate "EtherCAT device", see chapter
EtherCAT device setup [} 32]. In this case the CU2508 port represents the first EtherCAT device in the
system. It is capable of Distributed Clocks and can therefore operate as a reference clock in the strand.
The combination of EtherCAT cable redundancy and Distributed Clock function is possible by combining two
such EtherCAT ports using the "TwinCAT cable redundancy" supplement (subject to charge).
Time-controlled send/receive (in preparation)
The frame forwarding in the CU2508 can be subjected to precise time control by the local clock:
• the driver or the user application specifies the downlink port via which the frame is to be sent by the
CU2508 and when.
These data are added by the driver to each frame as additional information.
• each frame received by the CU2508 at a Downlink port is supplemented by receipt information
(receiving port, time) and forwarded to the controller via the uplink.
The local hardware-based clock in the CU2508 then controls the sending of the frames with a high temporal
quality. In this way, the CU2508 permits the construction of a real-time Ethernet network (TwinCAT
Publisher/Subscriber, Ethernet/IP, Profinet etc.), even if the control device cannot guarantee hard real-time
when sending the protocol data. However, the control device must be able to deliver or accept the data with
sufficient speed.
The time controller uses the 64-bit time format familiar from the EtherCAT Distributed Clocks system:
resolution 1 ns, starting from 1.1.2000 00:00 and thus adequate for ~584 years
The time stamp information (sending and receiving) is for the time being only evaluated by the CU2508
driver and is not available to the user application.
As the start of an Ethernet frame, the SFD (Start of Frame Delimiter) is evaluated according to the
IEEE802.3 standard.
EoE and TCP/IP
The CU2508 is connected to the IPC via the Gbit interface. This Ethernet interface appears in the operating
system/Windows of the IPC with its properties (IP address, IP mask etc.). From the point of view of the
operating system, therefore, there is "only" this network connection via which telegrams can be sent or
received. The CU2508 driver can now either convey data traffic from the operating system level to a
Real-time Ethernet port multiplier Version: 2.6
Product overview
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