Sd Memory Card - Libelium Waspmote Technical Manual

SD Memory Card

23. SD Memory Card
Waspmote has external storage support such as SD (Secure Digital) cards. These micro-SD cards are used specifically to reduce
board space to a minimum.
Figure: Micro-SD card
Waspmote uses the FAT16 file system and can support cards up to 2GB. The information that Waspmote stores in files on the
SD can be accessed from different operating systems such as Linux, Windows or Mac-OS. There are many SD card models; any of
them has defective blocks, which are ignored when using the Waspmote's SD library. However, when using OTA, those SD blocks
cannot be avoided, so that the execution could crash.
Libelium implements a special process to ensure the SD cards we provide will work fine with OTA. The only SD cards that Libelium
can assure that work correctly with Waspmote are the SD cards we distribute officially.
Figure: SD Card slot
To communicate with the SD module we use the SPI bus. This bus is a communication standard used to transfer information
between electronic devices which accept clock regulated bit flow. The SPI includes lines for the clock, incoming data and
outgoing data, and a selection pin.
The SD card is powered through a digital pin from the microcontroller. It is not therefore necessary to use a switch to cut the
power, putting a low pin value is enough to set the SD consumption to 0μA.
To get an idea of the capacity of information that can be stored in a 2GB card, simply divide its size by the average for what a
sensor frame in Waspmote usually occupies (approx. 100 Bytes):
2GB/100B = 20 million measurements
The limit in files and directories creation per level is 256 files per directory and up to 256 sub-directories in each directory. There
is no limit in the number of nested levels.
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