Fat16

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Read changes.txt if you have used previous releases of this library.

Please read the html documentation for this library. Start with html/index.html and read the Main Page. Next go to the Files tab and read the documentation for Fat16Config.h. Finally go to the Classes tab and read the Fat16 class documentation.

If you wish to report bugs or have comments, send email to [email protected]

Arduinos access SD cards using the cards SPI protocol. PCs, Macs, and most consumer devices use the 4-bit parallel SD protocol. A card that functions well on A PC or Mac may not work well on the Arduino.

Most cards have good SPI read performance but cards vary widely in SPI write performance. Write performance is limited by how efficiently the card manages internal erase/remapping operations. The Arduino cannot optimize writes to reduce erase operations because of its limited RAM.

SanDisk cards generally have good write performance. They seem to have more internal RAM buffering than other cards and therefore can limit the number of flash erase operations that the Arduino forces due to its limited RAM.

Some Dane-Elec cards have a write speed that is only 20% as fast as a good SanDisk card.

The hardware interface to the SD card should not use a resistor based level shifter. Fat16 sets the SPI bus frequency to 8 MHz which results in signal rise times that are too slow for the edge detectors in many newer SD card controllers when resistor voltage dividers are used.

The 5 to 3.3 V level shifter for 5 V arduinos should be IC based like the 74HC4050N based circuit shown in the file SdLevel.png. The Adafruit Wave Shield uses a 74AHC125N. Gravitech sells SD and MicroSD Card Adapters based on the 74LCX245.

To install the library copy the Fat16 directory to the libraries subdirectory of the Arduino user directory. On Windows 7 this is <User Name>\Documents\Arduino\libraries. On earlier versions of the Arduino IDE use the hardware/libraries subdirectory of the Arduino IDE.

For the AtMega168 be sure to reduce the serial buffer size by setting RX_BUFFER_SIZE to 32 or less in hardware/cores/arduino/HardwareSerial.cpp. I use 16.

Fat16 assumes chip select for the SD card is the hardware SS pin. On a 168/328 Arduino this is pin 10 and on a Mega this is pin 53. If you are using another pin for chip select you will need call SdCard::init(speed, chipSelectPin) with second parameter set to the chip select pin.

If you have a shield like the SparkFun shield that uses pin 8 for chip select you would change the line: card.init(); to card.init(0, 8); in the SdFat examples.

You can also edit SdCard.h and change the default value for chip select. Replace SPI_SS_PIN with the new value for chip select in the following definition.

uint8_t const SD_CHIP_SELECT_PIN = SPI_SS_PIN;

For example to set SD_CHIP_SELECT_PIN to 8 for the SparkFun microSD shield: uint8_t const SD_CHIP_SELECT_PIN = 8;

The best way to restore an SD card's format is to use SDFormatter which can be downloaded from:

http://www.sdcard.org/consumers/formatter/

SDFormatter aligns flash erase boundaries with file system structures which reduces write latency and file system overhead.

SDFormatter does not have an option for FAT type so it may format small cards as FAT12.

The Fat16/examples directory has the following sketches. They are my debug sketches.

fat16AnalogLogger.pde - A simple data logger for one or more analog pins.

fat16append.pde - This sketch creates a large file by successive open/write/close operations using O_APPEND.

fat16bench.pde - A read/write benchmark.

fat16copy.pde - Copy the file created by fat16append.pde to the file ACOPY.TXT.

fat16GPS_CSVSensorLogger.pde - Ladyada's GPS logger modified to use the Fat16 library.

fat16GPSLogger_v3.pde - Ladyada's GPS logger modified to use the Fat16 library.

fat16info.pde - This Sketch attempts to initialize an SD card and analyze its format. Used for debug problems with SD cards.

fat16ls.pde - A test of the ls() file list function.

fat16print.pde - This sketch shows how to use the Arduino Print class with Fat16.

fat16read.pde - This sketch reads and prints the file PRINT00.TXT created by fat16print.pde or WRITE00.TXT created by fat16write.pde.

fat16remove.pde - This sketch shows how to use remove() to delete the file created by the fat16append.pde example.

fat16rewrite.pde - This sketch shows how to rewrite part of a line in the middle of the file created by the fat16append.pde example.

fat16tail.pde - This sketch reads and prints the tail of all files created by fat16append.pde, fat16print.pde and fat16write.pde.

fat16timestamp.pde - This sketch shows how to set file access, create, and write/modify timestamps.

fat16truncate.pde - This sketch shows how to use truncate() to remove the last half of the file created by the fat16append.pde example.

fat16write.pde - This sketch creates a new file and writes 100 lines to the file.

To access these examples from the Arduino development environment go to: File -> Examples -> Fat16 -> <Sketch Name>

Compile, upload to your Arduino and click on Serial Monitor to run the example.

You must use a standard SD card that has been formatted with a FAT16 file system.

Updated 2009-11-28