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Discussion Groups | Comp.Arch.Embedded | SD card in 4-bit mode

There are 3 messages in this thread.

You are currently looking at messages 0 to 3.

SD card in 4-bit mode - Jookie - 06:14 09-09-08

  Hello all,

I'm in a need for the higher transfer speeds with SD card, I'm running the
card at 25 MHz via SPI and it works well, but I still need higher transfer
speed.

I would like to use the 4-bit (parallel) mode of the communication with
the SD card, and I know that to do that one has to be the member of some SD
association and that only SPI mode is free... But since this is just a
hobby project for myself, I wouldn't mind breaking a small copyright for my
project or experiments.

So what is the problem? Is the 4-bit mode documented on the web, but you
can't use it legaly without paying the SD association, or there is no
public documentation and you need to pay a fee to get that documentation?

Regards,
 Jookie



Re: SD card in 4-bit mode - 09:26 10-09-08

Jookie <j...@kie.sk> wrote:
> So what is the problem? Is the 4-bit mode documented on the web, but you
> can't use it legaly without paying the SD association, or there is no
> public documentation and you need to pay a fee to get that documentation?

Nowadays you can download a simplified SD card spec for free, which
should be enough to use the cards in 4-bit mode. The spec omits some
hardware details, I guess so that you can't implement a controller
without a license.

If you need to implement the controller yourself, you can now download
the complete MMC system specification for free. AFAIK the two standards
aren't 100% compatible, at least when it comes to the high capacity
modes. Hopefully someone will correct me on that if I'm wrong.

-a

Re: SD card in 4-bit mode - MisterE - 09:39 10-09-08

"Jookie" <j...@kie.sk> wrote in message 
news:J...@giganews.com...
>  Hello all,
>
> I'm in a need for the higher transfer speeds with SD card, I'm running the
> card at 25 MHz via SPI and it works well, but I still need higher transfer
> speed.
>
> I would like to use the 4-bit (parallel) mode of the communication with
> the SD card, and I know that to do that one has to be the member of some 
> SD
> association and that only SPI mode is free... But since this is just a
> hobby project for myself, I wouldn't mind breaking a small copyright for 
> my
> project or experiments.
>
> So what is the problem? Is the 4-bit mode documented on the web, but you
> can't use it legaly without paying the SD association, or there is no
> public documentation and you need to pay a fee to get that documentation?

you set the the bus width via a few commands, I think sandiks docos have 
full details:
http://www.sandisk.com/Assets/File/OEM/Manuals/SD_SDIO_specsv1.pdf