adding a memory card to single-chip CPU

Mar 13, 2006 3 Replies
D

I'd like to add a removable memory card ( 128Mbytes or more I suppose ) to my tentative design, which uses the AT91SAM7x128 processor. As far as I can see the processor has no in-built assistance for communicating with a CF, MMC/SD, smartmedia or any other external flash device I might consider.



In particular I can't instantly see that I can output a read or write strobe so I may have to bit-bash the whole dratted read and write cycle... though you may know better.



I've designed ( on another project), but never built, a smartmedia interface, which requires about 12 pins. I could handle that, and I could use it for a soldered-on NAND flash if I liked too, so that's a bonus.



I believe the MMC/SD card has a serial mode which looks a bit SPI-like, but I know nothing more about it. Anyone know if you can actually use all the memory over that interface? Is it SPI?



The ideal would be a 2cm square device with a nice simple interface, which corresponds to a nice simple interface in the 7x CPU which I don't happen to be using. :-)



Anyone got any suggestions, or know of any Atmel/other application notes on the subject?



David


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J

On 13/03/2006 the venerable David Collier etched in runes:

I have interfaced ATmega128 to SD memory cards with the built in SPI interface. It's very easy with a couple of caveats. Firstly SD is 3.3V so M128 signals have to be fed through a couple of resistors and secondly it is not possible to use the #CS pin of the SPI interface as the SD card pulls this line low to indicate its presence. You need to use another pin.

Progressive resources have a useful FAT 16 library for M128 but I dont know if it is ported to the ARM yet. Have a look at

formatting link

John B Delete \'spam blocker\' to reply direct
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U

Everyday Electronics starting May 2005 had a good article on how to talk to CF cards... they were ultimately looking to get a PIC talking to it so with some tweaks, it sounds right up your street.

H
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T

Circuit Cellar covered this in detail a few months ago, using a 3-wire interface to memory cards.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/
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