3.15.1. MMC or SD operation

The MMC socket provides nine pins that connect to the card when it is inserted into the socket. (The nine-way socket is compatible with Secure Digital cards. However MultiMedia Cards use only seven of the nine pins.)

The socket contains two switches that are operated by inserting or removing the card. These are used to provide signaling on the nCARDIN and WPROT signals.

The function of the interface signals depends on whether an MMC or SD card is fitted. Both card types default to MMC mode but the SD card has an additional operating mode called widebus mode. Table 3.13 lists the use of the signals for both modes of operation.

Table 3.13. MMC/SD interface signals

Signal Widebus mode (SD card only)MMC mode (default)
MCIDAT3card detect/Data(3)chip select (active LOW)
MCICMDcommand/Responsecommand/Response
MCICLKclockclock
MCIDAT0data (0)data
MCIDAT1data (1)not used
MCIDAT2data (2)not used
nCARDINcard presence detect (active LOW)card presence detect (active LOW)
WPROTcard write-protection detect card write-protection detect

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