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What are the main differences between interfacing with SD and MMC devices?

2006-04-12 by darcy_will

Hi all,

Please excuse my ignorance of these issues.  I'm only just looking 
to begin playing with an Olimex LPC2148 dev kit having finally got 
the thing up and running with GCC/Insight etc...

Because the development board comes with an MMC (and SD?) slot I 
just assumed this is probably the type of flash device I'd end up 
using in our "product" (just a home project at the moment).  Having 
had a bit of a look around it's fairly easy to see that SD has 
overtaken MMC as far as price and availability go.  This certainly 
makes me think that SD is the flash type to go with.

If a FAT16/32 file system is implemented on this kit (using 
something like RDCF or EFSL for example), how easy is it to swap the 
flash cards between MMC and SD?  I've seen that SD and MMC can both 
use the same transfer protocol to the uC, but does the change in 
format also require an overhaul of the flash driver on the uC?

This is kind of a dual purpose question...  
a) Can the same driver used for MMC cards be used for SD?
b) if not, how different is the interface?

I'm not looking to be able to use both types of flash cards on the 
same project...  more curious as which is the one to go with.

There certainly *seem* to be more examples out there for MMC than 
SD...  In fact I haven't found any examples of SD file systems on 
the LPC21xx range.  Maybe I'm just not looking hard enough?  :)

Any help would be greatly appreciated!

Cheers
Darcy

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