VLANs or multiple ethernet cards?

I'm planning a robot retrofit, which will use Ethercat servo drives, a mesa 7i94T (serving a 7i84U and 2x 7i73 boards), and an ethernet link to an existing Fanuc 31i-B5.

• I've read that ethercat can be run through a switch without difficulty, but I couldn't find anything regarding its behavior through a VLAN.
• I can't find any information on what one can actually do with mesa's ethernet links. I plan to connect some limit switches, discrete interfacing with the Fanuc 31i-B5, the user interface system, and some analog measurement through the mesa board set. Thus, it seems that real-time performance isn't critical.
• The link to the Fanuc 31i-B5 is ordinary switchable/routable ethernet with no special requirements. I plan to check the 31i-B5's operating mode and the state of certain R and X registers via FOCAS, but if that is delayed for a few hundred milliseconds I don't anticipate trouble.

Is it practical to use 3 VLANs and a managed switch to connect these sets of devices to a computer with one physical ethernet port, or should I add extra ethernet cards? I want to use COTS gear wherever possible.

I have not actually tested it but I would think it would work just fine doing tagged on the PC ethernet port with subinterfaces (or however linux does it these days its been a minute) and exposing those segments as untagged to the devices. I don't think there is a way for the devices to even know its a vlan somewhere when hanging on an untagged port.

You'll need not-overlapping subnets on the vlans if you need IP connectivity over and above just ethernet frames.

JacobRush wrote:

tagged on the PC ethernet port with subinterfaces (or however linux does it these days its been a minute) and exposing those segments as untagged to the devices.
 

That's what I figured.

If I were to run LinuxCNC on a raspberry pi (whatever variant), I could potentially handle the UI (buttons, maybe some LEDs, the MPG) through the GPIO pins, and move the digital/analog I/O to ethercat devices, which would completely eliminate the Mesa hardware. That would still require ethercat on one VLAN and general purpose ethernet on another.

I might try it each way and see what works.

As long as network latency isn't impacted theoretically it may work.
The RPi will suffer somewhat if you require the use of a base thread for some input requirement. Personally I think an SPI for simplicity a 7c81, which is simple to replicate using off the shelf Spartan 6 Dev boards, maybe a better option for IO.

The mesa website has a manual for each and every board, so that should give you enough with what you can do with mesa ethernet, a base card is very easily extended via smart serial cards. The access at register level is documented in each manual.
While obtaining mesa hardware outside of the US due to postage, it can almost double the price for items coming Down Under they are solid and reliable and very well supported

I wasn't able to make the ethercat master use the vlan interface, only the physical.
On the other hand I don't really know what I am doing, so a test is advised.