Breakout Board for microSD Card

Breakout Board for microSD Card

Breakout Board for microSD Card

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MicroSD memory cards (originally known as TransFlash) provide a compact and inexpensive way to add gigabytes of non-volatile storage to a project. All SD cards support communication over the SPI (Serial Peripheral Interface) bus, making it straightforward to interface one of these cards with an SPI-capable microcontroller.

This carrier board makes it easy to connect to a microSD card by breaking out all of the contacts from a microSD card socket into two rows of 0.1?-spaced pins. The board measures only 0.8? × 0.7?, and a set of breakaway 0.1? male header strips (one 1×7 and one 1×4) is included, which can be soldered in to use the board with breadboardsperfboards, or 0.1? female connectors. (The headers might ship as a single 1×11 piece that can be broken in two).

Using the breakout board

Since many microcontrollers have built-in SPI interfaces, most hobbyist projects communicate with Secure Digital cards in SPI bus mode. (The alternative SD bus mode is proprietary, and a license from the SD Association is required for access to the full specifications.) Where applicable, the pins on this board are labeled according to their functions in SPI mode.

All of the microSD card’s power pins and all of the signal pins necessary to interface with the card through SPI are available along the right side of the board. The left side of the board exposes duplicate power pins, along with two additional signal lines (DAT1 and DAT2) that are not needed for SPI communication but are used in 4-bit SD bus mode. The DAT1 pin also serves as an interrupt pin (IRQ) in SDIO devices. (Note that if you are using this module in a breadboard, you might want to solder header pins into both sides of the board for added stability even if you only plan to use the SPI pins.)




Power and logic ground
VDDSupply voltage (2.7 V to 3.6 V for standard microSD cards)
CDCard detect. When a card is inserted, this pin is floating; when no card is inserted, it is shorted to ground. A pull-up resistor can be used to pull the line high when a card is present.
SPI modeSD mode
DIData in (MOSI)CMDCommand/response
DOData out (MISO)DAT0Data (bit 0)
CSChip select (active low)DAT3Data (bit 3)

Interrupt (active low; SDIO devices only)
Data (bit 1)
Interrupt (active low; SDIO devices only)
ReservedDAT2Data (bit 2)
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