MultiMediaCardTM
Figure 4-3 MultiMediaCard State Diagram (Data Transfer Mode)
The command SELECT_DESELECT_CARD (CMD7) is used to select one card and place it in the
Transfer State. If a previously selected card is in the Transfer State its connection with the host is
released and it will move back to the Stand-by State. Only one card can be, at any time, in the Transfer
State. A selected card is responding the CMD7, the deselected one does not respond to this command.
When CMD7 is sent including the reserved relative card address “0x0000”, all cards transfer back to
Stand-by State. This command is used to identify new cards without resetting other already acquired
cards. Cards to which an RCA has already been assigned, do not respond to the identification
command flow in this state. All the data communication in the Data Transfer Mode is consequently a
point-to point communication between the host and the selected card (using addressed commands).
All addressed commands are acknowledged by a response on the CMD line. All read commands (data
is sent from the card via data lines) can be interrupted at any time, by a stop command. The data
transfer will terminate and the card will stop or start working on the next command. The DAT bus line
signal level is high when no data is transmitted. A transmitted data block consists of a start bit (LOW),
followed by a continuous data stream.
The data stream contains the net payload data (and error correction bits if an off-card ECC is used).
The data stream ends with an end bit (HIGH). The data transmission is synchronous to the clock signal.
The payload for block-oriented data transfer is preserved by a CRC check sum (refer to Chapter
“Cyclic Redundancy Check (CRC)”).
4.9.1 Block Read
The basic unit of data transfer is a block whose maximum size is defined in the CSD
(READ_BLK_LEN). A CRC is appended to the end of each block ensuring data transfer integrity.
READ_SINGLE_BLOCK (CMD17) starts a block read and after a complete transfer the card goes back
to Transfer State. READ_MULTIPLE_BLOCK (CMD18) starts a transfer of several consecutive blocks.
Two types of multiple block read transactions are defined (the host can use either one at any time):
* Open-ended Multiple block read : The number of blocks for the read multiple block operation is not
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