Types of data logger
1) just store the data on the card
2) Acquire the analogical signals and store it on the card (preferable)
1)Format the card from windows with a known FAT, when you format Windows always prompt you the kind of FAT that you want use (FAT, FAT16, FAT32).
2)Filling the card with a binary file that contains the number FF or 00.
3)Know the exact location of the file start , communicate it to the PIC and start to write.