To enable embedded microprocessors to access Secure Digital memory cards via a SPI port, this small circuit
board provides a Micro SD card connector and 5V-to-3.3V level translation
circuitry as well as a low-drop-out 3.3 Volt regulator to supply the
operating voltage for the Micro SD card from a 5V-powered mcu board.
The MISO output pin has a true 5 V logic high level.
The required pull-up resistances for the SPI lines and decoupling capacitors for the supply voltage complete the circuit, so it is ready to connect to any 5V microprocessor without additional components.
Micro SD and Micro SD HC cards are available for 1 to 2 Euro/US$ per gigabyte, thus offering a very economical and robust data storage solution for all embedded systems with an SPI port.
Circuit board dimensions: 19 x 35 mm, with gold finished contacts, 0.1" pitch (2.54 mm)
Operates with 5 V supply from the MCU board.
Communication with the SD card consists of four lines:
CS : Chip Select
CLK : Data Clock
MOSI : master out - slave in
MISO : master in - slave out
An additional pin is used for detecting card insertion. It is high when the card is removed and low when inserted.
The card holder fits MicroSD and MicroSDHC (the only difference between the two is at the firmware level that the microcontroller has to consider: the HC cards use block addresses, the low density cards use byte addresses: a BlockRead at position 1024 will return block 3 on a low density card and block 1024 on a HC card).
5V MicroSD-Card Module mechanical description
For a detailed description of the SPI protocol and the command codes needed to get the SD card talking,
see the SanDisk manuals:
Example code in C for accessing SD cards from a microprocessor (tested with HCS09, HCS12 and 56f8000E DSP)
with a primitive file system
signal description for SPI interface configuration
TinyFat File System by ChaN : complete FAT16 implementation, also works with high-capacity SDHC cards
Sandisk OEM Manuals