Thank you John, It seems like my scope was loading it quite a bit and is now giving much better readings using x10 probes. The signals bellow are set to 400 kHz using 1kOhm pull-ups
<https://lh3.googleusercontent.com/-7duEugw1hxo/WswdBXMl_HI/AAAAAAAAJIQ/yZV_JKhLjvoSQQTOxiZOy2iJ_N1NgEciQCLcBGAs/s1600/ADS00016.BMP> <https://lh3.googleusercontent.com/-FrqmGorE0l0/WswdOl9P7HI/AAAAAAAAJIU/p3SAy8cPGhIV1gu4vT3A09qAQhFoqfDQgCLcBGAs/s1600/ADS00014.BMP> On Friday, April 6, 2018 at 9:49:48 AM UTC+12, john3909 wrote: > > Yeah, I agree there is something else going on here. with a 1K resistor, > the signals should not have a slow rising time. The rise time doesn’t look > like a capacitor, but I agree, that is about the only explanation that > would cause the rise time to slow like this. Maybe the I2C part is faulty. > Try plugging in another I2C part to see if the problem persists. > > Regards, > John > > > > > > On Apr 5, 2018, at 8:02 AM, Graham <gra...@flex-radio.com <javascript:>> > wrote: > > > It looks like you have some extra capacitance on the bus. There should > not be any capacitors bridging the I2C data and clock lines. Some of the > third-party universal interface cards have extra capacitance, so take those > off. > > I have never heard of an I2C part with built in pull-up resistors. > > Do to the multi-drop nature of the I2C bus, pull up resistors are almost > always external. There are some "weak pull up" resistors you could turn on > in the BBB, but are too high in value for most applications. > > I suggest you read up on how to select pull up resistors for an I2C bus. > Phillips (now NXP) initially developed the bus and has good documentation. > Google: NXP I2C bus documentation > > But the short answer is that for a 3.3V bus, resistors in the range of > 1.2K to 3.3K should work fine. The value is not critical. You want to pull > 1 to 3 mA through the resistor when the bus is low. > > --- Graham > > == > > > > > > > > -- > 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...@googlegroups.com <javascript:>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/a8ed3ca6-d286-4d29-8dc1-8851aa384db3%40googlegroups.com > > <https://groups.google.com/d/msgid/beagleboard/a8ed3ca6-d286-4d29-8dc1-8851aa384db3%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > > > -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/00a745ff-a990-4f42-9fb5-5b6e92861043%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
