Peter C. Wallace wrote: > On Mon, 29 Oct 2007, Jon Elson wrote: > >>The idea is that 100 mbit/sec ethernet is fast. What other >>RS485 device do you have that runs that fast? > > > Of course a RS-485 link can have smaller packets, and may actually have much > better real time performance. (a single 10 MBps RS-485 link will have much > better performance than 100 BT Ethernet connected to a single encoder) > > Also 100BT with its MLT3 encoding is not as electrically robust as isolated > RS-485 or 10BT. > > Ethernet is great for broadcast but I don't think so good for collecting data > from a large number of separate real time devices (say encoders) > Yes, I think this would be a bad way to do things. Having a single motion control board that interfaces by Ethernet, as I have been envisioning, would have a lot of advantages. It keeps the sampling of all the encoders synchronized, it compresses all the information interchange into a couple packets, it saves on hardware. Putting a separate ethernet interface into each encoder is a great way to sell a lot of hardware. > I think Ethernet would be a really good way to connect a multi channel motion > controller to a PC where the large packet size is not such nuisance. You > would > likely need a separate Ethernet card from the main network connection. RTnet, for instance, gets around this to some extent. But, that is one way to do it, have 2 ethernet ports on the computer, one for RT, one for the local net. Otherwise some kind of router needs to be used to keep outside traffic from flooding the RT segment.
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