Ethercat Hub and the NI-9144

[DailyDose]

Hello,

Using the NI-9144.  I understand EthercCAT can daisy chain and what not, but daisy chaining our system is completely nonsensical.  Are there hubs available?  I've read about the CU1128 but cannot find that on sale outside of eBay anywhere.  Do typical network switches work as well?  Does NI sell something?  Can the NI-9144 even work with a Hub?

Oh... and my LabVIEW question is... do you prefer indicator and controls as big boxes or small boxes on your block diagram.  (I forget, terminals or something?)

[zhengchen]

Hi DailyDose,

I am sorry that I didn't get your idea clearly. As you said that the daisy chaining is not available with your system, which physical topology will be used in your system? NI EtherCAT doesn't support the star topology. 

[DailyDose]

We're using NI EtherCAT.  The NI-9144 can obviously daisy chain.  Because of the environment and the distance the Chassis are from each other, it does not make sense to daisy chain one to the next.  I'm asking is there a hub or switch or some type of Ethercat router available?  Or would any typical router/switch work?

[rolfk]

No I don't think a normal Hub will work at all. EtherCAT is very much like a long train. During startup phase each slave is queried by the master about its bus image (its own variables mapped into a byte stream) and all those partial images are then appended together in one big long frame like the wagons in a train. After the setup phase the bus changes to the running state and the frame (train) is then sent through the wire and each device adds its own image to the correct place (wagon) in the train. A hub would have to act as EtherCAT master towards any network subnet that is connected to it and combine the individual trains from each subnet into a bigger train that it then sends as slave to the real master. That's a lot more complicated then what typical network hubs do and requires a hub with specific EtherCAT support. The chance that such a hub just works with all the different EtherCAT devices out there is pretty small and that might be the reason, that you can't really buy it anymore, as the manufacturer abandoned the product because of to many support hassles with different EtherCAT devices.

But this device is from Beckhoff and I don't think they stopped selling such a device. Looking on the Beckhoff site they certainly still seem to sell CU1123, CU1124 and CU 1128. Contact your local Beckhoff sales office for that.