adding a memory card to single-chip CPU

[David Collier]

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

 

[John B]

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

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

http://www.prllc.com

 

[[email protected]]

On Mon, 13 Mar 2006 11:16 +0000 (GMT Standard Time),

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

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

 

[Tim Wescott]

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

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

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