At 06:04 AM 8/18/2008, you wrote:
>To address both items at once:
>
>My past experience with I2C is rather old... and pretty much limited to
>the port-expander and ADC/DAC hardware.  That experience pretty much got
>me thinking along the lines of each device has a hardwired address and
>there isn't much flexibility on most parts as to what addresses are
>available to you.   I've now corrected my thinking in that regards...
>
>As far as how these are connected together...  These are devices which
>are intended to be din-rail (or wall) mounted right next to each other
>with a short, but pin-limited jumper cable between them.  I'm also
>providing power and ground via that jumper.   I figure the jumper will
>likely be a 6p6c or a 8p8c connector.

I2C has come a long way in recent years. One great change has been 
the use of the basic I2C spec in a variety of other bus systems. For 
lots of info and for details of a variety of buffer / extender 
products see http://www.hendersonsemiconductor.com . They also offer 
application notes talking about speed-up circuits and the other buses.

John


>  Right now, I'm toying with the
>idea of using power, ground, and data on a multidrop serial bus, and
>assigning each device a globally-unique serial number at manufacture
>time so that the probed order can be preserved from run to run.  The
>3-wire bus will let me use a 6p6c, but double up each pin so that I can
>use either "reversed" or "straight" 6p6c jumpers.
>
>That said, I'm still open to ideas..
>
>-forrest
>
>Alan B. Pearce wrote:
> >>> 5) Slaves should be able to be detected by the master, and should not
> >>> have to have addresses set via dip-switches or other means.   Globally
> >>> (factory set) unique addresses are ok (aka 1-wire style), dip-switches
> >>> are not (aka i2c is not an option).
> >> Nothing that you have said actually rules out I2C. If you use the
> >> 'general call' address, you can discover the devices on the bus and
> >> then dynamically assign an I2C address. In reality it depends almost
> >> entirely on how dynamic you little network is, if it is highly
> >> dynamic then this may result in a slow start-up each time.
> >
> > That is my reaction also. You don't say how these devices are 
> connected into
> > the network, are they in a card cage, separate devices connected 
> by cables,
> > some other scheme? None of this removes the possibility of having an
> > appropriate number of pins on the connection plug that sets the device
> > address for that node, which gets around your dislike of dip switches.
> >
> > The other possibility I thought of would be the CAN bus, which 
> has a rather
> > different way of setting who receives what, but does have limited message
> > length, which requires a bit of thinking about to send long messages.
> >
>
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