Delkin Blog

The serial interface of SD cards has made them hugely popular in both consumer and industrial devices for OEMs. The SD Card Association tightly controls the specifications of SD cards, including the SD card pinout, so there are universal standards for everything from physical interfaces to command protocols that make integration seamless and easy. SD cards are designed to meet the needs of both consumer and industrial markets and their differing budgets. Most consumer devices rely on MLC flash memory, while industrial devices use SLC flash.  An SD card pinout can vary depending on the mode of the card.

SD Card Modes

SD cards automatically use SD mode for the bus protocol. SD mode offers high speeds and bus widths of between one and four bits in clock serial mode. Users can override the SD mode default, however, to use the card in SPI mode. SPI mode is best suited for applications in which a slower, simpler card is ideal. The speed difference with SD and SPI modes can be significant, as the card can only operate at one bit in SPI mode.

SD Card Pinouts in SD Mode

Each SD card, regardless of mode, has 9 pins, with the eighth pin at one end and the ninth at the other. When running in SD mode, the pinout and signal functions look like this:

8. DAT1 – Data bit one
9. DATA0/DO – Data bit 0
10. Vss2 – Ground 2
11. CLK – Clock
12. Vcc – Supply voltage
13. Vss1 – Ground 1
14. CMD/DI – Command line
15. DAT3/CS – Data bit 3
16. DAT2 – Data bit 2

With this pinout, SD cards can support normal and high speed modes.

SD Card Pinouts in SPI Mode

SPI mode offers simpler functioning, and not every pin has a connection. The pinout and the signal functions are as follows:

8. RSV – Reserved
9. DO – Master In/Slave Out (or MISO)
10. Vss – Ground
11. CLK – Clock
12. Vcc – Supply voltage
13. DI – Master Out/Slave In (MOSI)
14. CS – Chip Select
15. NC – No connection
16. RSV – Reserved

Do you have questions about SD card pinouts and using SD cards for flash storage? Delkin is here to provide the information you need and help you evaluate all of your options for industrial-grade, rugged memory. Talk to our product team today.