SD Card Capacity Limit

I've seen a lot of expandable MP3 players with SD card slots and most of them allow a 1GB card max. I'm sure not every expandable player is implemented the same way, but what could be some of the reasons these players have a 1GB limit?

Reply to
TastyWheat
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SD cards have an inherent limit of 2 GB which is increased to 32 GB in the v2 spec, but that uses a different sector addressing scheme. 1 GB may be the practical limit of FAT16 (with 16K allocation).

Peter

Reply to
Peter Dickerson

Okay, well assume I had a FAT32 formatted SDHC (v2) card with 32GB. What component(s) can keep me from using this card in an embedded system? Or maybe just tell me exactly what I would need to read data from such a card.

Reply to
TastyWheat

Software in the microcontroller.

Reply to
larwe

But this isn't a factor if reading and writing sectors directly??? As in not using a conventional DOS style FAT??

I'm in the process of implementing an interface to allow old computers to have access to a hard disk in their native storage format. All they ask for is to be able to read and write 512byte sectors. If the native format's limit is say 128MBytes, then I shall just split a single 2GB SD card into 16 virtual storage mediums.

How they manage their allocation tables is upto them, all I'm doing is giving them access to the SD card's sectors as requested.

Reply to
Aly

the

Well, the 2.0 specs haven't been released yet, or at least I can't find them, so I can't directly say why SDHC cards aren't backwards compatible. Since SDHC cards will be using FAT32 it sounds like the blocksize is the only difference (unless the pin configuration has changed).

Reply to
TastyWheat

Not if the larger cards require (say) an extra address byte when you tell them what sector to r/w.

Reply to
larwe

in the

may be the

No, the v2 spec isn't public. There is no hardware difference that I can tell, nor do I know where the 32 G limit comes from (unless FAT32 has that limit). The main difference I see with high capacity cards is the read/write commands are rejigged to take sector numbers instead of byte address. So your software has to identify the card as v2, then see if it is HC and then change how parameters are sent.

Peter

Reply to
Peter Dickerson

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