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RM0351 SD/SDIO/MMC card host interface (SDMMC)
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41 SD/SDIO/MMC card host interface (SDMMC)
41.1 SDMMC main features
The SD/SDIO MMC card host interface (SDMMC) provides an interface between the APB2
peripheral bus and MultiMediaCards (MMCs), SD memory cards and SDIO cards.
The MultiMediaCard system specifications are available through the MultiMediaCard
Association website, published by the MMCA technical committee.
SD memory card and SD I/O card system specifications are available through the SD card
Association website.
The SDMMC features include the following:
• Full compliance with MultiMediaCard System Specification Version 4.2. Card support
for three different databus modes: 1-bit (default), 4-bit and 8-bit
• Full compatibility with previous versions of MultiMediaCards (forward compatibility)
• Full compliance with SD Memory Card Specifications Version 2.0
• Full compliance with SD I/O Card Specification Version 2.0: card support for two
different databus modes: 1-bit (default) and 4-bit
• Data transfer up to 50 MHz for the 8 bit mode
• Data and command output enable signals to control external bidirectional drivers.
Note: 1 The SDMMC does not have an SPI-compatible communication mode.
2 The SD memory card protocol is a superset of the MultiMediaCard protocol as defined in the
MultiMediaCard system specification V2.11. Several commands required for SD memory
devices are not supported by either SD I/O-only cards or the I/O portion of combo cards.
Some of these commands have no use in SD I/O devices, such as erase commands, and
thus are not supported in the SDIO protocol. In addition, several commands are different
between SD memory cards and SD I/O cards and thus are not supported in the SDIO
protocol. For details refer to SD I/O card Specification Version 1.0.
The MultiMediaCard/SD bus connects cards to the controller.
The current version of the SDMMC supports only one SD/SDIO/MMC4.2 card at any one
time and a stack of MMC4.1 or previous.
41.2 SDMMC bus topology
Communication over the bus is based on command and data transfers.
The basic transaction on the MultiMediaCard/SD/SD I/O bus is the command/response
transaction. These types of bus transaction transfer their information directly within the
command or response structure. In addition, some operations have a data token.
Data transfers to/from SD/SDIO memory cards are done in data blocks. Data transfers
to/from MMC are done data blocks or streams.
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