Overo expansion connector SD interface

[Andrew Kohlsmith (lists)]

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.

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[Søren Steen Christensen]

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


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