On Apr 2, 2010, at 5:10 PM, DJ Delorie wrote:
I2C is driven from both ends of the bus, so if you want to use the
pull-ups as terminators, use two resistors, each twice the resistance,
one at each end.
I2C pullups are generally a few kohms, far above any practical characteristic
impedance, so they will have essentially no effect on ringing due to drive.
They don't have enough drive capacity to produce ringing on upward transitions.
On downward transitions the driver output resistance will be more important for
damping.
I've never heard of anyone worrying about ringing on I2C though...
I presume that I2C device makers choose drivers weak enough and receivers slow
enough to avoid problems on reasonably sized boards.
John Doty Noqsi Aerospace, Ltd.
http://www.noqsi.com/
j...@noqsi.com
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