On 2/18/14, 10:49 AM, "k...@cranehome.info" <k...@cranehome.info> wrote:
>I think I have seen those on my scope during I2C transactions as well. >They look like little shark fins that sometimes get high enough to be >seen as a logic 1. They have no impact on the device as it's just the >transition time between when the master is done transmitting the device >address and starting to send data. The data line is released by the >device but the master has not started to place data on the wire yet so >the line starts to float back up via the pull-up. In your photo, it >happens on the falling edge of the 9th clock bit and it's gone before the >rising edge of the 10th clock so it's not being read as data. > >Stronger pull-ups will just assist the runt in rising faster since the >lower resistance allows the data line capacitance to be charged faster. >On the scope you'd see the shark-fin start getting taller as you reduce >the resistance. Your logic analyzer is just showing the brief time that >the runt was interpreted as a logic 1 by the logic analyzer. Data isn't >clocked in until SCL goes from low to high. > >I think what you are chasing there is a red herring. The Logic analyzer >shows both data values being what they ought to be. Unless your lines are very long, there is probably nothing wrong with your I2C signals. My guess is you have a long ground wire on your oscilloscope probe and this is causing the ringing. Use a high speed probe (small distance between measurement tip and ground pin) and I¹m sure the signals will look a lot cleaner. The long ground wire is acting like an antenna. Regards, John > >-- >For more options, visit http://beagleboard.org/discuss >--- >You received this message because you are subscribed to the Google Groups >"BeagleBoard" group. >To unsubscribe from this group and stop receiving emails from it, send an >email to beagleboard+unsubscr...@googlegroups.com. >For more options, visit https://groups.google.com/groups/opt_out. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
