Delkin Blog

Understanding the SD Card Interface

 

Secure Digital cards, or SD cards, are widely used in consumer and industrial markets. The SD card interface is simple and widely compatible, making it an easy choice for designers and OEMs. The Secure Digital Association determines the design specifications, and these specs are available only to members of the group. For members, the exact design protocols of the physical interface can be downloaded, which can be helpful to OEMs who are implementing SD cards into their systems. SD cards are available in both SLC NAND flash industrial formats and commercial MLC NAND flash designs. Here is what you need to know about the SD card interface.

 

Intelligent Controller

The flash management operations in SD cards are handled by an intelligent controller, and data transfers occur serially in 512-byte blocks between the host system and the card. For cards with capacities of 2Gbytes or lower, the defined file system is FAT12/16. Cards with capacities of 4Gbytes or more use FAT32.

 

This is just like CF and PC cards, which are familiar to many OEMs. However, the pinout for SD cards is different than with those designs. SD cards use nine contact pads instead of pins for contact. For legacy compatibility with MMC cards, the 9-pad is placed below the 1-pad and is positioned out of alignment and with a greater width. From top to bottom, the pinout looks like this:

8: DAT1

7: DAT0/DO

6: Vss2

5: CLK

4: Vcc

3: Vss1

2: CMD/DI

1: DAT3/CS

9: DAT2

 

Voltages

Although lower voltages are available, the standard voltage range of SD cards is 2.7-3.3V. The lower voltage models are generally designed specifically for consumer electronic devices that require this kind of reduced voltage range. Standard voltages are used for industrial grade SD cards.

 

Bus Information

SD cards operate with a default bus protocol of SD mode. However, if a simpler or slower bus is needed, the card can be configured for SPI mode. While in SPI mode, SD cards operate in one-bit bus widths. In SD mode, the cards use a serial clock mode for bus widths of between one and four bits.

 

When the SD card is put into SD or SPI mode, it cannot be switched to the other mode while power is applied. However, the modes can be switched during a power cycle as needed.

 

Delkin’s product team can answer all of your questions about the SD card interface and other industrial grade embedded storage options. Contact us today for more information or to request an engineering sample.

 

Contact

  • This field is for validation purposes and should be left unchanged.

Related Posts

How Delkin Helped One Customer Overcome SD Card Lifespan Concerns

  The evolution of flash technology has been a good thing for developers and end...

Delkin Technology Flash Endurance
What Are the Benefits of High Endurance Flash Storage?

  When choosing flash memory, one of the most important factors to consider is endurance....

Delkin Devices mSATA
Flash Disk SATA Drives

  Flash disk SATA drives are solid state drives or hard disk drives that use...

Flash Storage Encryption

  Every file stored on a flash device is important, but some information requires more...

Understanding Industrial SD for Parking Technologies

  Parking technologies have progressed far beyond simply turning a car between two lines. Public...

High Temperature Storage Test

  For industrial devices, having storage that functions in high temperature environments is crucial. Storage...

Understanding Embedded Memory Systems
Taking a Closer Look at Embedded Module Options

  An embedded module is a self-contained component that is installed inside of a larger...

Wide Temperature Range SSD- Antarctic Research Station
Answering Questions about SLC Temperature Ranges

  There are many reasons why industrial application designers and engineers opt for SLC flash...

Power Fail
The Benefits of Low Power SSD Drives

  Many industrial device engineers have moved away from hard disk drives, or HDDs, for...

Controls and Automation Application- Delkin Devices
Understanding Embedded Flash Technology

  Flash technology is a popular form of memory for many applications, including small, portable...