SD card in 4-bit mode

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

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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.


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you set the the bus width via a few commands, I think sandiks docos have full details:

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