SD Card
SD, miniSD, and microSD cards use the same signals, but not always the same contact numbers. They can communicate over the native SDIO / 4-bit SD bus or the simpler SPI bus commonly used with microcontrollers.
Caution: on the classic interface, VDD is generally between 2.7 and 3.6 V. Signaling normally uses 3.3 V, but may switch to 1.8 V with compatible UHS‑I or LVS modes. Observe the voltages supported by both the card and host; never directly apply 5 V logic levels.
The three form factors
- SD: 9 contacts
- miniSD: 11 contacts, including reserved and unconnected contacts 10 and 11
- microSD: 8 contacts
SDIO / 4-bit SD bus wiring
| Signal | SD | miniSD | microSD | Purpose |
|---|---|---|---|---|
| DAT2 | 9 | 9 | 1 | Data bit 2 |
| DAT3 | 1 | 1 | 2 | Data bit 3 / detection |
| CMD | 2 | 2 | 3 | Command and response |
| VSS | 3 and 6 | 3 and 6 | 6 | Ground |
| VDD | 4 | 4 | 4 | 3.3 V supply |
| CLK | 5 | 5 | 5 | Clock |
| DAT0 | 7 | 7 | 7 | Data bit 0 |
| DAT1 | 8 | 8 | 8 | Data bit 1 / SDIO interrupt |
SPI wiring
| SPI signal | SD | miniSD | microSD | Purpose at the card |
|---|---|---|---|---|
| CS | 1 | 1 | 2 | Active-low select |
| MOSI / DI | 2 | 2 | 3 | Data into the card |
| VSS | 3 and 6 | 3 and 6 | 6 | Ground |
| VDD | 4 | 4 | 4 | 3.3 V supply |
| SCLK | 5 | 5 | 5 | SPI clock |
| MISO / DO | 7 | 7 | 7 | Data from the card |
| Unused | 8 and 9 | 8 to 11 | 1 and 8 | Reserved / not connected |