Information Technology Reference
In-Depth Information
5
MultiMediaCard
Protocol
SPI provides a protocol for sending and receiving bytes, but the interface
assumes nothing about the contents of the bytes being transferred. The
MultiMediaCard specification defines commands to use in SPI communica-
tions. The host uses the commands to retrieve information about a card and
its status, to send control information to a card, and to read and write data
in the card's storage media. This chapter introduces the MultiMediaCard
commands and shows how to implement the commands in firmware. A host
can use the same commands and firmware to access SD Cards.
Command and Response Formats
Each MultiMediaCard command has a defined format for the command, a
response, and any additional data the command sends or requests. On the
SPI bus, the DataIn line carries commands and data sent by the host, and
the DataOut line carries responses and data sent by the MultiMediaCard.
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