DocID018909 Rev 11 1011/1731
RM0090 Secure digital input/output interface (SDIO)
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31 Secure digital input/output interface (SDIO)
This section applies to the whole STM32F4xx family, unless otherwise specified.
31.1 SDIO main features
The SD/SDIO MMC card host interface (SDIO) provides an interface between the APB2
peripheral bus and MultiMediaCards (MMCs), SD memory cards, SDIO cards and CE-ATA
devices.
The MultiMediaCard system specifications are available through the MultiMediaCard
Association website at http://www.jedec.org/, published by the MMCA technical committee.
SD memory card and SD I/O card system specifications are available through the SD card
Association website at http://www.sdcard.org.
CE-ATA system specifications are available through the CE-ATA workgroup website.
The SDIO 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
• Full support of the CE-ATA features (full compliance with CE-ATA digital protocol
Rev1.1)
• Data transfer up to 48 MHz for the 8 bit mode
• Data and command output enable signals to control external bidirectional drivers.
Note: The SDIO does not have an SPI-compatible communication mode.
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. In addition, several commands are different between
SD memory cards and SD I/O cards and thus are not supported in the SDIO. For details
refer to SD I/O card Specification Version 1.0. CE-ATA is supported over the MMC electrical
interface using a protocol that utilizes the existing MMC access primitives. The interface
electrical and signaling definition is as defined in the MMC reference.
The MultiMediaCard/SD bus connects cards to the controller.
The current version of the SDIO supports only one SD/SDIO/MMC4.2 card at any one time
and a stack of MMC4.1 or previous.
31.2 SDIO bus topology
Communication over the bus is based on command and data transfers.
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