- 3V - This is the power pin. MicroSD cards must use 3.3V, so take care to only hook 3.3V to this pin. Hooking 5V or VBAT to this pin will damage your microSD card.
- GND - common ground for power and logic.
Common Logic Pins
- DET - Detect whether a microSD card is inserted. This pin is connected to GND internally when there's no card, but when one is inserted it is pulled up to 3V with a 4.7kΩ resistor. That means that when the pin's logic level is False there's no card and when it's True there is.
SPI Logic Pins
If you're using SPI to connect to your SD cards, the pins have the following functions:
- CLK - This is the SPI Clock pin / SCK Serial Clock, its an input to the chip.
- SO - this is the Serial Out / Microcontroller In Serial Out pin, for data sent from the SD card to your processor.
- SI - this is the Serial In / Microcontroller Out Serial In pin, for data sent from your processor to the SD card. Its an input to the chip and can use 3 - 5V logic.
- CS - this is the Chip Select pin, drop it low to start an SPI transaction. Its an input to the chip and can use 3 - 5V logic.
Pull ups are provided on all SPI logic pins.
SDIO Logic Pins
If you're using SDIO to connect to your SD cards, the pins have the following functions:
- CLK - The SDIO clock pin. A clock signal is sent by the microcontroller to the SD card on this pin.
- CMD - A bidirectional pin for communication between the microcontroller and the SD card, used for commands and information.
- 4 Data pins - Four bidirectional pins for communication between the microcontroller and the SD card, used for transferring bulk data. Take care to wire these in the correct order! The silk screen legends read: D0, D1, DAT2, D3.
Pull ups are provided on all SDIO logic pins.