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AT89C51ED2 FAt16
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jameslys
Tue Sep 02 2008, 07:00AM
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can anyone tell me how to access the fat16 in sd card using spi?
where to find the fat16 accessing details?
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Ajay
Tue Sep 02 2008, 02:01PM
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Jameslys, are you able to get your card working?
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jameslys
Tue Sep 02 2008, 04:48PM
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my card is successfully initialized, can read the CID register. i try to read the address 0x00 of a fat16 formatted card, it returns all 0. i dont know why.
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Ajay
Wed Sep 03 2008, 01:57AM
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you have to read sectors, not addresses..

I hope you know the complete structure of how FAT file system is organized, so once you read the MBR of card, you will come to know the location of root directory.

Official information on FAT16 by Microsoft:

Better explained.. (recommended)
FAT16 Structure Information

[ Edited Wed Sep 03 2008, 02:01AM ]
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jameslys
Wed Sep 03 2008, 03:21AM
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some of the address contains more than one byte data, such as maximum root directories and sectors per FAT, which are containing 2 bytes data. For spdat, one byte data is received and store each time, i use array to store the data. how to i combine 2 different array elements to calculate the sector address?
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Ajay
Wed Sep 03 2008, 03:57AM
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i give you example to combine two bytes to form 16-bit value.

CODE:
unsigned char byte1 = 0x28;
unsigned char byte2 = 0x35;
unsigned int combined;

combined = byte1;
combined = (combined << 8) | byte2;
//combined will now have value 0x2835
 

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jameslys
Wed Sep 03 2008, 04:14AM
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thanks a lot
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jameslys
Wed Sep 03 2008, 04:31AM
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if i need to combine 4 bytes to form a 32-bit value, is it like that?

unsigned char byte1 = 0x28;
unsigned char byte2 = 0x35;
unsigned char byte3 = 0x30;
unsigned char byte4 = 0x26;
unsigned int combined;

combined = byte1;
combined = (combined << 8) | byte2;
combined = (combined << 8)| byte3;
combined = (combined << 8) | byte4;

is the code above correct? Can i declare combined as unsigned long combined
And combine the 3 code sentences as:?
combined = (combined << 24) | byte2 | byte3 | byte4;
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Ajay
Wed Sep 03 2008, 05:57AM
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the first code is fine..

you can shorten it like this..
CODE:
combined = byte1;
combined = (combined << 24) | (byte2<<16) | (byte3<<8) | byte4
 

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jameslys
Fri Sep 05 2008, 06:23PM
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If the fat16 is fragmented, how to get the next cluster value after i accessing the starting cluster? If the current cluster is the end of file, is it will show that the next cluster is FFF8 - FFFH? If the is multiple files in the fat16 farmatted sd card and a structure is declared for user selection later, how to add the root directory of each files into the structure by skipping the empty entries. And how to determine that current sector read is the last sector in the cluster? is it by comparing to the size of cluster?

[ Edited Fri Sep 05 2008, 06:27PM ]
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