Secure Digital (SD) card initialization in SPI mode

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I'm attempting to interface to an SD card using an AT89S8252 MCU.  I'm
using an 74LS125 to convert between 5V and 3.3V.  The hardware seems to
be ok since I *do* get a response from the card but I'm having problems
initializing the card in SPI mode.

I am sending 96 clock cycles initially and then I send a CMD0.
Everything I've read suggests that CMD0 should initially respond with
0x01 at which point I can issue CMD1 to take the card out of idle mode.
Sometimes this works.  But most of the time it doesn't work.

I usually get 0xFC back from the card and it never returns another
value until I eject the card and re-insert it.  At that point CMD0
returns 0x03 and never goes to 0x01.  Sometimes I find that if I insert
the card into an SD card reader I have and then reinsert it into my
hardware that the card works as expected (CMD0 returns 0x01, I then
issue CMD1 which returns 0x01 for awhile and then returns 0x00).

The 0x03 response to CMD0 suggests to me it is in idle mode and
reporting an "erase/reset" error.  I've been unable to determine what
exactly that means.

At this point I'm running out of ideas of what I could be doing wrong.
I've looked at some code that was written for Atmel AVRs and it appears
I'm doing the same thing.  And like I said sometimes it works.  But
most of the time it seems the card is in some kind of strange state
that I can't get it out of.

If anyone has any ideas I would be very interested in some suggestions.
Thanks,
Craig


Re: Secure Digital (SD) card initialization in SPI mode
Never mind.  I found the problem.  A short between the CS line and
another line was causing the SD card to always be selected.  Bad thing.
Problem solved.


Re: Secure Digital (SD) card initialization in SPI mode
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Where did you get the spec for the SD card interface?
What kind of sustained transfer rates are you getting?
-howy


Re: Secure Digital (SD) card initialization in SPI mode

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The specs are downloadable at http://www.sandisk.com

Rene
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