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adding a memory card to single-chip CPU

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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David Collier
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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 

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John B

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John B

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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unclewobbly

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

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Tim Wescott

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