From: Andrew K. (M. L. Account) <ak...@mi...> - 2009-10-19 16:45:04
|
Good afternoon, I'd like to add a normal-sized SD card to an expansion board I'm designing for the Overo Earth. I see the SD signals on the expansion connector, but have a few questions regarding it. 1) Is this SD interface also connected to the on-Overo microSD interface? 2) If so, what GPIO should I tie the SD card detect switch to so that the Overo will see when a card is inserted into my SD card socket? 3) Am I correct in assuming that SD card signals must be level-shifted to 1.8V for the Overo? 4) Do I need source termination on these lines? What value if so? 5) Why is there an 8-bit interface? I thought SD/MMC cards were 4-bit maximum. I think that's it. :-) -A. |
From: Søren S. C. <li...@ss...> - 2009-11-03 22:37:00
|
Hi Andrew, > 1) Is this SD interface also connected to the on-Overo microSD > interface? These are not the same - AFAIR the microSD is MMC1 while the expansion connector is MMC3 > 2) If so, what GPIO should I tie the SD card detect switch to so that > the Overo will see when a card is inserted into my SD card socket? Normally the Card Detect is connected to the CD1 and CD2 pins on TPS5950 - These are however not brought out on the Gumstix connectors => You might need to do some SW changes in order to fix this and you can therefore choose which GPIO might fit you best. GPIO0-31 however are in an always on OMAP-power domain, whereas the other GPIO are in a domain which can be switched off for power-saving, so I would choose one of the lower ones in case you don't need them for other stuff... > 3) Am I correct in assuming that SD card signals must be level-shifted > to 1.8V for the Overo? Correct - MMC3 only supports 1V8 operation > 4) Do I need source termination on these lines? What value if so? AFAIK: Should not be needed... > 5) Why is there an 8-bit interface? I thought SD/MMC cards were 4-bit > maximum. Newer versions of the MMC spec (version 4 and onwards AFAIR) opens for an 8-bit wide bus Good luck with your project Søren --- SSC Solutions ApS - Denmark - www.ssc-solutions.dk |