Getting started with FAT Filesystem on SD/MMC cards over SPI

Robert S. Grimes rsg at
Mon Sep 15 14:04:41 UTC 2008

Sebastian Huber wrote:
> Some cards require in the initialization procedure that they see some
> clock cycles without an active chip select.  So the LibI2C functions
> have to satisfy this (in this sequence):
> start: The driver occupies the bus.
> set transfer mode: The driver sets the transfer mode.
> write/read: Write/read to/from the device with INACTIVE chip select
> (drives the clock).
> send address: Activates the appropriate chip select.
> write/read: Write/read to/from the device ACTIVE chip select.
> stop: Deactivates the corresponding chip select and releases the bus.
Hi Sebastian,

Thanks for the additional information.  I'm in the setup mode (hardware 
and software), so it'll be a few days before I'm get to this, but I'll 
let you know how it goes.


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