1 | /* Arduino SdFat Library
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2 | * Copyright (C) 2009 by William Greiman
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3 | *
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4 | * This file is part of the Arduino SdFat Library
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5 | *
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6 | * This Library is free software: you can redistribute it and/or modify
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7 | * it under the terms of the GNU General Public License as published by
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8 | * the Free Software Foundation, either version 3 of the License, or
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9 | * (at your option) any later version.
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10 | *
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11 | * This Library is distributed in the hope that it will be useful,
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12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 | * GNU General Public License for more details.
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15 | *
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16 | * You should have received a copy of the GNU General Public License
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17 | * along with the Arduino SdFat Library. If not, see
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18 | * <http://www.gnu.org/licenses/>.
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19 | */
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20 |
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21 | /**
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22 | \mainpage Arduino SdFat Library
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23 | <CENTER>Copyright © 2009 by William Greiman
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24 | </CENTER>
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25 |
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26 | \section Intro Introduction
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27 | The Arduino SdFat Library is a minimal implementation of FAT16 and FAT32
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28 | file systems on SD flash memory cards. Standard SD and high capacity
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29 | SDHC cards are supported.
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30 |
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31 | The SdFat only supports short 8.3 names.
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32 |
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33 | The main classes in SdFat are Sd2Card, SdVolume, and SdFile.
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34 |
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35 | The Sd2Card class supports access to standard SD cards and SDHC cards. Most
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36 | applications will only need to call the Sd2Card::init() member function.
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37 |
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38 | The SdVolume class supports FAT16 and FAT32 partitions. Most applications
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39 | will only need to call the SdVolume::init() member function.
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40 |
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41 | The SdFile class provides file access functions such as open(), read(),
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42 | remove(), write(), close() and sync(). This class supports access to the root
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43 | directory and subdirectories.
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44 |
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45 | A number of example are provided in the SdFat/examples folder. These were
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46 | developed to test SdFat and illustrate its use.
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47 |
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48 | SdFat was developed for high speed data recording. SdFat was used to implement
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49 | an audio record/play class, WaveRP, for the Adafruit Wave Shield. This
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50 | application uses special Sd2Card calls to write to contiguous files in raw mode.
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51 | These functions reduce write latency so that audio can be recorded with the
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52 | small amount of RAM in the Arduino.
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53 |
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54 | \section SDcard SD\SDHC Cards
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55 |
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56 | Arduinos access SD cards using the cards SPI protocol. PCs, Macs, and
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57 | most consumer devices use the 4-bit parallel SD protocol. A card that
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58 | functions well on A PC or Mac may not work well on the Arduino.
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59 |
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60 | Most cards have good SPI read performance but cards vary widely in SPI
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61 | write performance. Write performance is limited by how efficiently the
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62 | card manages internal erase/remapping operations. The Arduino cannot
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63 | optimize writes to reduce erase operations because of its limit RAM.
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64 |
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65 | SanDisk cards generally have good write performance. They seem to have
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66 | more internal RAM buffering than other cards and therefore can limit
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67 | the number of flash erase operations that the Arduino forces due to its
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68 | limited RAM.
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69 |
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70 | \section Hardware Hardware Configuration
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71 |
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72 | SdFat was developed using an
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73 | <A HREF = "http://www.adafruit.com/"> Adafruit Industries</A>
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74 | <A HREF = "http://www.ladyada.net/make/waveshield/"> Wave Shield</A>.
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75 |
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76 | The hardware interface to the SD card should not use a resistor based level
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77 | shifter. SdFat sets the SPI bus frequency to 8 MHz which results in signal
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78 | rise times that are too slow for the edge detectors in many newer SD card
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79 | controllers when resistor voltage dividers are used.
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80 |
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81 | The 5 to 3.3 V level shifter for 5 V Arduinos should be IC based like the
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82 | 74HC4050N based circuit shown in the file SdLevel.png. The Adafruit Wave Shield
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83 | uses a 74AHC125N. Gravitech sells SD and MicroSD Card Adapters based on the
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84 | 74LCX245.
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85 |
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86 | If you are using a resistor based level shifter and are having problems try
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87 | setting the SPI bus frequency to 4 MHz. This can be done by using
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88 | card.init(SPI_HALF_SPEED) to initialize the SD card.
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89 |
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90 | \section comment Bugs and Comments
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91 |
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92 | If you wish to report bugs or have comments, send email to fat16lib@sbcglobal.net.
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93 |
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94 | \section SdFatClass SdFat Usage
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95 |
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96 | SdFat uses a slightly restricted form of short names.
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97 | Only printable ASCII characters are supported. No characters with code point
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98 | values greater than 127 are allowed. Space is not allowed even though space
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99 | was allowed in the API of early versions of DOS.
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100 |
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101 | Short names are limited to 8 characters followed by an optional period (.)
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102 | and extension of up to 3 characters. The characters may be any combination
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103 | of letters and digits. The following special characters are also allowed:
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104 |
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105 | $ % ' - _ @ ~ ` ! ( ) { } ^ # &
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106 |
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107 | Short names are always converted to upper case and their original case
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108 | value is lost.
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109 |
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110 | \note
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111 | The Arduino Print class uses character
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112 | at a time writes so it was necessary to use a \link SdFile::sync() sync() \endlink
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113 | function to control when data is written to the SD card.
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114 |
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115 | \par
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116 | An application which writes to a file using \link Print::print() print()\endlink,
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117 | \link Print::println() println() \endlink
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118 | or \link SdFile::write write() \endlink must call \link SdFile::sync() sync() \endlink
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119 | at the appropriate time to force data and directory information to be written
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120 | to the SD Card. Data and directory information are also written to the SD card
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121 | when \link SdFile::close() close() \endlink is called.
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122 |
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123 | \par
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124 | Applications must use care calling \link SdFile::sync() sync() \endlink
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125 | since 2048 bytes of I/O is required to update file and
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126 | directory information. This includes writing the current data block, reading
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127 | the block that contains the directory entry for update, writing the directory
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128 | block back and reading back the current data block.
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129 |
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130 | It is possible to open a file with two or more instances of SdFile. A file may
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131 | be corrupted if data is written to the file by more than one instance of SdFile.
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132 |
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133 | \section HowTo How to format SD Cards as FAT Volumes
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134 |
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135 | You should use a freshly formatted SD card for best performance. FAT
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136 | file systems become slower if many files have been created and deleted.
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137 | This is because the directory entry for a deleted file is marked as deleted,
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138 | but is not deleted. When a new file is created, these entries must be scanned
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139 | before creating the file, a flaw in the FAT design. Also files can become
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140 | fragmented which causes reads and writes to be slower.
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141 |
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142 | Microsoft operating systems support removable media formatted with a
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143 | Master Boot Record, MBR, or formatted as a super floppy with a FAT Boot Sector
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144 | in block zero.
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145 |
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146 | Microsoft operating systems expect MBR formatted removable media
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147 | to have only one partition. The first partition should be used.
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148 |
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149 | Microsoft operating systems do not support partitioning SD flash cards.
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150 | If you erase an SD card with a program like KillDisk, Most versions of
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151 | Windows will format the card as a super floppy.
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152 |
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153 | The best way to restore an SD card's format is to use SDFormatter
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154 | which can be downloaded from:
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155 |
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156 | http://www.sdcard.org/consumers/formatter/
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157 |
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158 | SDFormatter aligns flash erase boundaries with file
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159 | system structures which reduces write latency and file system overhead.
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160 |
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161 | SDFormatter does not have an option for FAT type so it may format
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162 | small cards as FAT12.
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163 |
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164 | After the MBR is restored by SDFormatter you may need to reformat small
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165 | cards that have been formatted FAT12 to force the volume type to be FAT16.
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166 |
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167 | If you reformat the SD card with an OS utility, choose a cluster size that
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168 | will result in:
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169 |
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170 | 4084 < CountOfClusters && CountOfClusters < 65525
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171 |
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172 | The volume will then be FAT16.
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173 |
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174 | If you are formatting an SD card on OS X or Linux, be sure to use the first
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175 | partition. Format this partition with a cluster count in above range.
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176 |
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177 | \section References References
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178 |
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179 | Adafruit Industries:
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180 |
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181 | http://www.adafruit.com/
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182 |
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183 | http://www.ladyada.net/make/waveshield/
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184 |
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185 | The Arduino site:
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186 |
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187 | http://www.arduino.cc/
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188 |
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189 | For more information about FAT file systems see:
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190 |
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191 | http://www.microsoft.com/whdc/system/platform/firmware/fatgen.mspx
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192 |
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193 | For information about using SD cards as SPI devices see:
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194 |
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195 | http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
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196 |
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197 | The ATmega328 datasheet:
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198 |
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199 | http://www.atmel.com/dyn/resources/prod_documents/doc8161.pdf
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200 |
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201 |
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202 | */
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