SD Card Interface FAQs and Answers
The Secure Digital Card Association established the specifications required for all Secure Digital (SD) memory cards, including the command protocols and the physical SD card interface. This simplifies the application development process for engineers, as the strict guidelines eliminate unexpected deviations and support predictable, reliable operations. Here is a look at the answers to a few common questions about the SD card interface.
How can I access the official SD card interface specifications?
The Secure Digital Association maintains tight control over the specifications. It’s possible to discover some information about the SD card interface specs that is publicly available. However, developers are advised to become members of the Secure Digital Association in order to gain full access to all of the specifications. This also provides access to new developments, which can be essential information for OEMs that are incorporating SD cards into their applications.
How do SD card operations work?
Intelligent controllers are responsible for supporting the data transfer between the SD card and the host system, and for managing the flash operations. The data transfer is achieved serially in 512 byte blocks. The defined file system depends on the specific capacity of the SD card. SD cards capable of storing 4GB and more follow the FAT32 file system. For cards with capacities of 2GB or less, the file system is FAT12/16.
What is the default bus protocol?
The SD card interface follows a default bus protocol of SD mode. However, OEMs may configure the card to operate in SPI mode. If reconfigured for SPI mode, the SD card will only operate in 1-bit mode. If the SD card maintains the default bus protocol of SD mode, then it will operate with bus widths of 1 to 4 bits, in clock serial mode.
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