I hope this is ok under the PIC tag. I'm using a pic for it! I'm looking
at the contents of the sectors of an SD card formatted FAT16. I'm finding
the boot record for partition #1 at sector 0x5f. At offset 22 decimal is
supposed to be a 16 bit word with sectors/FAT, according to various
documents I've found on the web. This location has 0x00f2. The next word
(at offset 24 decimal) is supposed to be sectors/track (which seems
meaningless on an SD card). The value I'm finding there is 0x0020.

I find the first FAT at sector 0x60. I find the second FAT at sector 0x80.
I'm trying to figure out how one determines how long the FAT is (so I can
figure out where the second FAT starts and where the root directory starts
after it). It SEEMS we should somewhere have a "clusters per FAT" since
that would tell us how many FAT table entries there are. With
"sectors/FAT" we'd need to divide by the number of sectors per cluster
(which I'm finding in the boot record at offset 13 decimal as 0x04).

It IS interesting that the value at offset 24 (supposedly sectors/track)
has a value of 0x20, which appears to be the size of the FAT (first one at
sector 0x60, second at 0x80).

So... can someone suggest exactly what I should be looking at to determine
the size of the FAT?

THANKS!

Harold


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