A.6. MMC and SD flash card interface

The MMC/SD card sockets provides nine pins that connect to the MultiMedia Card or Secure Digital card when it is inserted into the socket. Figure A.6 shows the pin numbering and signal assignment. In addition, the socket contains switches that are operated by card insertion and provide signaling on the nCARDIN and WPROT signals.

Figure A.6. MMC/SD card socket pin numbering, J21

MMC/SD card socket pin numbering, J21

The MMC card uses seven pins, and the SD card uses all nine pins. The additional pins are located as shown in Figure A.6 with pin 9 next to pin 1 and pins 7 and 8 spaced more closely together than the other pins. Figure A.7 shows an MMC card, with the contacts face up.

Figure A.7. MultiMedia Card (MMC)

MultiMedia Card (MMC)

Table A.5 lists the signal assignments.

Table A.5. MultiMedia Card interface signals

Pin SignalFunction in SD widebus modeFunction in MCI mode
1MCIDATA3Data Chip select
2MCICMDCommand/responseData in
4MCIVDDSupply voltageSupply voltage
7MCIDATA0Data 0Data out
10 (DET A)CARDINCard insertion detectCard insertion detect
11 (DET B)WPROTWrite protect status Write protect status

Insert and remove the card as follows:


Insert the card into the socket with the contacts face down. Cards are normally labeled on the top surface with an arrow to indicate correct insertion.


Remove the card by gently pressing it into the socket. It springs back and can be removed. Removing the card in this way ensures that the card detection switches within the socket operate correctly.

Copyright © 2005-2011 ARM Limited. All rights reserved.ARM DUI 0411D