AVR-Chat

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