Peter C. Wallace wrote: > On Tue, 30 Oct 2007, Javid Butler wrote: > > >>Date: Tue, 30 Oct 2007 19:36:35 -0600 >>From: Javid Butler <[EMAIL PROTECTED]> >>Reply-To: "Enhanced Machine Controller (EMC)" >> <emc-users@lists.sourceforge.net> >>To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >>Subject: Re: [Emc-users] Ethernet I/O >> >>Jon wrote- >> >> >>>Given all the required overhead to read and write multiple >>>packets, it is already pretty close to chewing up a whole >>>millisecond, and there's no way it could handle even 5 KHz >>>servo update rate. So, I really don't think CAN is a good >>>candidate. >> >>I agree. The thread started because of concern about the parport going away >>on newer machines, and how to replace it. I have not seen any computers with >>a CAN interface built in, which would defeat the whole purpose. We could >>consider USB, but that has problems as well and met with resistance >>upthread. Ethernet is relatively easy, affordable and available, and as Jon >>mentioned before is isolated. > > > Not arguing for CAN, but Ethernet being built-in is not a great advantage > unless there are 2 channels built in, since real time Ethernet (real time > meaning fast enough to close a servo loop) will not get along with normal > Ethernet traffic and a network connection is almost a necessity, requiring a > add-in card in most cases. Not much different from the parallel port case, > though faster. RTnet solves this problem by time division multiplexing the ethernet, but then you need some other machine to have the dual ethernet ports to work as a router. But, you only need one.
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