AVR-Chat

On Fri, 21 Jul 2006 12:26:31 -0700
 Ned Konz <ned@bike-nomad.com> wrote:
> Jim Wagner wrote:
> > I would use async serial over RS422/485 with simple
> packets
> > containing a CRC.
> > 
> > One of the big problems with TWI in this situation is
> that
> > the addressed device has to ack in a particular bit
> time.
> > In a long wire system, this means that you have to slow
> > down the clock. Further, the transceiver is not built
> to
> > drive hi-C loads which you get with long wires. 
> 
> Look at the new version of I2C ("Fast Mode Plus") from
> Philips: better 
> drive capability, longer wires...
> 
> The new drivers can drive 4000 pF (as opposed to 400 pF
> for the last 
> generation).
> 
>
http://www.standardics.philips.com/literature/leaflets/i2c/pdf/fast.mode.pca9665.pdf
>
http://www.standardics.philips.com/literature/other/i2c/pdf/selection.guide.pdf
> 
> > Also, the master is supposed to provide the clock. If
> you
> > have multiple "masters" (how else would you have
> > "collisions"), then you would have multiple devices
> trying
> > to inject clocks onto a single clock line. This all
> sounds
> > to me like a prescription for big problems.
> 
> The I2C spec provides for multiple masters.
> 
> 
> Thanks,
> -- 
> Ned Konz
> ned@bike-nomad.com
> http://bike-nomad.com

My recollection from the avrfreaks list is that there is an
identified problem with many or all AVRs in multi-master
TWI situations.

Jim

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