Message: 3 Date: Fri, 02 Apr 2010 13:46:19 -0400 From: Jim <[1]...@k4gvo.com> Subject: gEDA-user: OT: I2C pullup resistor location To: gEDA user mailing list <[2]geda-u...@moria.seul.org> Message-ID: <[3]4bb62d6b.7050...@k4gvo.com> 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:j...@k4gvo.com 2. mailto:geda-user@moria.seul.org 3. mailto:4bb62d6b.7050...@k4gvo.com
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