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2 CRC bytes
Busy
low
Start
bit
End
bit
Start
bit
End
bit
CMD
Data
CLK
Architecture
1271
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multimedia Card (MMC)/Secure Digital (SD) Card Controller
26.2.3 Protocol Descriptions
The MMC/SD controller follows the MMC/SD protocol for completing any kind of transaction with the
multimedia card and secure digital cards. For more detailed information, refer to the supported MMC and
SD specifications in
.
26.2.3.1 MMC/SD Mode Write Sequence
and
show the signal activity when the MMC/SD controller is in the MMC/SD mode
and is writing data to a memory card. The same block length must be defined in the MMC/SD controller
and in the memory card before initiating a data write. In a successful write protocol sequence, the
following steps occur:
•
The MMC/SD controller requests the CSD content.
•
The card receives the command and sends the content of the CSD register as its response.
•
If the desired block length, WRITE_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 states from standby to transfer.
•
The card receives the command and sends responses to the command.
•
The MMC/SD controller sends a write command to the card.
•
The card receives the command and sends responses to the command.
•
The MMC/SD controller sends a block of data to the card.
•
The card sends the CRC status to the MMC/SD controller.
•
The card sends a low BUSY bit until all of the data has been programmed into the flash memory inside
the card.
Figure 26-5. MMC/SD Mode Write Sequence Timing Diagram
Table 26-2. 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 CPU to the card.
CMD RSP
Command response: The card sends a 6-byte response of type R1 to acknowledge the WRITE_BLOCK to the
CPU.
DAT BLK
Data block: The CPU 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 CPU 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.