Datasheet

SAM9263 [DATASHEET]
Atmel-6249N-ATARM-SAM9263-Datasheet_14-Mar-16
750
39.8 MultiMedia Card Operations
After a power-on reset, the cards are initialized by a special message-based MultiMedia Card bus protocol. Each
message is represented by one of the following tokens:
 Command: A command is a token that starts an operation. A command is sent from the host either to a
single card (addressed command) or to all connected cards (broadcast command). A command is
transferred serially on the CMD line.
 Response: A response is a token which is sent from an addressed card or (synchronously) from all
connected cards to the host as an answer to a previously received command. A response is transferred
serially on the CMD line.
 Data: Data can be transferred from the card to the host or vice versa. Data is transferred via the data line.
Card addressing is implemented using a session address assigned during the initialization phase by the bus
controller to all currently connected cards. Their unique CID number identifies individual cards.
The structure of commands, responses and data blocks is described in the MultiMedia-Card System Specification.
See also Table 39-4 on page 751.
MultiMedia Card bus data transfers are composed of these tokens.
There are different types of operations. Addressed operations always contain a command and a response token.
In addition, some operations have a data token; the others transfer their information directly within the command or
response structure. In this case, no data token is present in an operation. The bits on the DAT and the CMD lines
are transferred synchronous to the clock MCI Clock.
Two types of data transfer commands are defined:
 Sequential commands: These commands initiate a continuous data stream. They are terminated only when
a stop command follows on the CMD line. This mode reduces the command overhead to an absolute
minimum.
 Block-oriented commands: These commands send a data block succeeded by CRC bits.
Both read and write operations allow either single or multiple block transmission. A multiple block transmission is
terminated when a stop command follows on the CMD line similarly to the sequential read or when a multiple block
transmission has a pre-defined block count (See “Data Transfer Operation” on page 753.).
The MCI provides a set of registers to perform the entire range of MultiMedia Card operations.
39.8.1 Command - Response Operation
After reset, the MCI is disabled and becomes valid after setting the MCIEN bit in the MCI_CR Control Register.
The PWSEN bit saves power by dividing the MCI clock by 2
PWSDIV
+ 1 when the bus is inactive.
The two bits, RDPROOF and WRPROOF in the MCI Mode Register (MCI_MR) allow stopping the MCI Clock
during read or write access if the internal FIFO is full. This will guarantee data integrity, not bandwidth.
The command and the response of the card are clocked out with the rising edge of the MCI Clock.
All the timings for MultiMedia Card are defined in the MultiMedia Card System Specification.
The two bus modes (open drain and push/pull) needed to process all the operations are defined in the MCI
command register. The MCI_CMDR allows a command to be carried out.
For example, to perform an ALL_SEND_CID command:
Host Command N
ID
Cycles Response High Impedance State
CMD S T Content CRC E Z ****** Z S T CID Content Z Z Z