TMS320DM644x DMSoC Multimedia Card (MMC)/Secure Digital (SD) Card Controller User's Guide

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2 CRC bytes
Busy
low
Start
bit
End
bit
Start
bit
End
bit
CMD
Data
CLK
2.3.2 MMC/SD Mode Read Sequence
Peripheral Architecture
Figure 5. MMC/SD Mode Write Sequence Timing Diagram
Table 2. MMC/SD Mode Write Sequence
Portion of the
Sequence Description
WR CMD Write command: A 6-byte WRITE_BLOCK command token is sent from the ARM to the card.
CMD RSP Command response: The card sends a 6-byte response of type R1 to acknowledge the WRITE_BLOCK to the
ARM.
DAT BLK Data block: The ARM writes a block of data to the card. The data content is preceded by one start bit and is
followed by two CRC bytes and one end bit.
CRC STAT CRC status: The card sends a one byte CRC status information, which indicates to the ARM whether the data has
been accepted by the card or rejected due to a CRC error. The CRC status information is preceded by one start
bit and is followed by one end bit.
BSY BUSY bit: The CRC status information is followed by a continuous stream of low busy bits until all of the data has
been programmed into the flash memory on the card.
Figure 6 and Table 3 show the signal activity when the MMC controller is in the MMC/SD mode and is
reading data from a memory card. The same block length must be defined in the MMC controller and in
the memory card before initiating a data read. In a successful read protocol sequence, the following steps
occur:
• The MMC/SD controller requests for the CSD content.
• The card receives the command and sends the content of the CSD register as its response.
• If the desired block length, READ_BL_LEN value, is different from the default value determined from
the response, the MMC/SD controller sends the block length command.
• The card receives the command and sends responses to the command.
• The MMC/SD controller requests the card to change state from stand-by to transfer.
• The card receives the command and sends responses to the command.
• The MMC/SD controller sends a read command to the card.
• The card drives responses to the command.
• The card sends a block of data to the ARM.
14 Multimedia Card (MMC)/Secure Digital (SD) Card Controller SPRUE30B – September 2006
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