Portable media memory cards use either SD/MMC or SPI mode communications protocol.
SD/MMC (Secure Digital/MultiMedia Card) cards are small, high-speed storage media for portable items such as digital cameras, mobile phones, netbook computers and similar devices. The communications protocol occurs in one of two modes: SD/MMC or SPI (Serial Peripheral Interface).
SD/MMC
These are similar cards that use the same communications protocol. SD was developed out of the MMC format. This protocol occurs in a question-and-answer format, controlled by the host or master, which sends commands to networks or single cards. These, in turn, send responses. Signals used are CLK, host to card clock, CMD, a bidirectional command/response signal, four bidirectional data signals, and power and ground signals.
SPI
SPI protocol consists of command, response and data blocks. At its simplest, communication in this format is divided into card initialization phase or data access phase. Signals begin with a low CS, or host to chip card signal, with data sent to the media card via MOSI (Master Out Slave In) line. Responses are received on the MISO (Master In Slave Out) line, with the CLK synchronizing the data.
Similarities
Both modes use single master/multiple slave structure to communicate with electronic devices or other media cards. At 20 to 25 Mhz, speed for both modes is high.
Tags: communications protocol, command response, Master Slave, Master Slave line, protocol occurs, Slave line
