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Peripheral Architecture

Figure 5. MMC/SD Mode Write Sequence Timing Diagram

CMD

 

 

 

 

 

 

Busy

2 CRC bytes

 

 

low

Data

 

 

 

Start

End

Start

End

bit

bit

bit

bit

CLK

 

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.

2.3.2MMC/SD Mode Read Sequence

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.

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Multimedia Card (MMC)/Secure Digital (SD) Card Controller

SPRUE30B –September 2006

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Texas Instruments TMS320DM644x manual MMC/SD Mode Write Sequence, 2 MMC/SD Mode Read Sequence, Portion Sequence Description