Bobby Clark wrote:
Did a little bit more checking. The smallest block size appears to be
512 bytes. The more common block size is 1024 bytes to 2048 bytes for
the larger cards.
While they may exist, I have not yet encountered a SD card with a block
length > 512 bytes. A 2GB SD card is accessed 512 bytes at a time even
though the block length is stated as 1024 bytes as a hack to calculate
the total number of bytes. The spec for SDHC cards is a fixed block
length = 512 bytes:
Simplified physical layer specification
<http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf>
(http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf)
pg 41:
"In High Capacity Cards, the 32-bit argument of memory access commands
uses the memory
address in block address format. Block length is fixed to 512 bytes,.."
Keep in ming that it is getting increasingly difficult to purchase SC
cards that are smaller than 2GB. Tomorrow it will be difficult to
purchase SD cards that are smaller than 4GB. So we may want to think
about getting used to SDHC cards.
Bob Furber
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