What is the minimum size micro controller that can support CAN? Every module, not matter how simple will need a uP that can suport whatever bus we choose. It would be great if we could get away with an 8-pin AVR "tiny" these sell for abut a buck each. I hate to use up a minimum 1 square inch of PCB space just to handle the system bus. But mmaybe CAN is easy and the software fits in 1K of on-chip flash? I don't know.
I really don't think we need anything so complex as CAN. A HYGE Open Counter system might have a dozen modules and I'd figure a typical number might be 2 or 4. With I2C we'd make up our own message dictioary and the uPs on each card would run at the "bit level" not using any kind of protocol stack. If noise on the wire is an issue then either every cards needs a balanced driver and we use twisted pair as out physical layer or we put the single ended i2c inside coax jumpers between cards. Again I don't care much what is used but I think we need 1) Reasonable speed 2) ALL cards should be peers with no "master" 3) in-band addressing 4) Small minimum size for the uP and low Flash memory footprint Can "CAN" do this? I'm worried about #2 and #4. I don't have time to read up on this right now and the Wiki article was not detailed enough On Wed, Dec 22, 2010 at 12:10 PM, Robert LaJeunesse <rlajeune...@sbcglobal.net> wrote: > The I2C bus is moderately well defined for the hardware interface, but hardly > at > all at the software level. This could be problematic for a system that > supports > multiple hardware configurations. It also uses single ended signalling which > creates RF noise if not treated extremely carefully. Might I suggest the use > of > a more robust, extensible interface with strong software support and > differential signalling? The best that comes to minde is 2-wire CAN based on > the > CANopen standard. See http://en.wikipedia.org/wiki/CANopen and > http://www.canopen.us/ > > Bob L. > > ________________________________ > From: Chris Albertson <albertson.ch...@gmail.com> > To: Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Wed, December 22, 2010 2:58:10 PM > Subject: Re: [time-nuts] Form factor > > The use of i...@c that I proposed was ONLY for module-to-module > communication. I wrote that none of the internal chips in a module > were to be exposed to the i2c bus. A module may very well have it's > own internal bus but that design detai needs to be hidden from the > rest of the system. > > In an open system built with modules yu realy, have to be careful to > never expose the inner working on a module. Else other modules come > to depend on the internal design of other modules and then you can > never upgrade of replace any of them because you have a circular > dependency loop or likely even multiple loops. So we have to be > carfull to never expose the kind of chip or it's internal bus address > between modules. > > ... > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- ===== Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
