Re: gEDA-user: I2C ringing

[Ouabache Designworks <z3qmtr45@xxxxxxxxx>]

     Message: 3
     Date: Fri, 02 Apr 2010 13:46:19 -0400
     From: Jim <[1]jim@xxxxxxxxx>
     Subject: gEDA-user: OT: I2C pullup resistor location
     To: gEDA user mailing list <[2]geda-user@xxxxxxxxxxxxxx>
     Message-ID: <[3]4BB62D6B.7050402@xxxxxxxxx>
     Content-Type: text/plain; charset=ISO-8859-1; format=flowed
     I'm building a backplane board that will have a processor board
     (master)
     and 8 slaves using I2C across the backplane.  Is there any advantage
     to
     placing the pullup resistors on the end of the backplane farthest
     from
     the processor board?  I recall installing active termination on the
     old
     S-100 bus backplanes to overcome problems with ringing, I think.
     It's
     been too long.
     Thanks,
     Jim.

   No advantage.
   S-100 (yes I also built them) had an active driver and fast enough
   edges so that
   the length was long enough to be a transmission line. I2C is open drain
   so that
   the active driver is the pullup resistor.
   You might put it at the end so that it makes an open trace easy to
   detect.
   John

References

   1. mailto:jim@xxxxxxxxx
   2. mailto:geda-user@xxxxxxxxxxxxxx
   3. mailto:4BB62D6B.7050402@xxxxxxxxx


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