From: Seth <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Friday, November 28, 2014 at 4:32 PM To: "[email protected]" <[email protected]> Subject: [beagleboard] Purpose of the GND_OSC zero ohm resistors?
> I'm looking at making my own version of the BBB for a custom project. I see a > note on Revision A6: "Noise issues were observed in other designs where the > clock oscillator was getting hit due to a suspected issue in ground bounce. A > zero ohm resistor was added to connect the OSC_GND to the system ground." A > second resistor was added in the next revision to the 32kHz crystal circuit. > > Could the GND_OSC nets be tied directly to DGND without zero ohm resistors? > Was the resistor used just in case the change caused problems and could be > left unpopulated if so? I see no issues in further revisions so I'd assume > that these changes fixed the issue, is that right? I'm asking because I > suspect there might be another reason why resistors were used instead of just > direct traces (like needing a 'single connection point' type of thing). Some > clarification would be helpful indeed. This is standard high speed digital layout design. If you don¹t isolate the OSC gnd, the PCB layout package will just flood all the gnd copper and then you will have digital switching noise traverse your OSC gnd and that will cause all kinds of problems. The concept is covered in books like "High Speed Digital Design: A Handbook of Black Magic² by Howard Johnson. Regards, John > > > Thanks, > -Seth > > -- > 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 [email protected]. > 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
