at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 376

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

MultiMedia Card
Operations
376
AT91RM3400
Figure 157. Mixing MultiMedia and SD Memory Cards
When the MCI is configured to operate with SD memory cards, the width of the data bus can
be selected in the MCI_SDCR register. Clearing the SDCBUS bit in this register means that
the width is one bit and setting it means that the width is four bits. In the case of multimedia
cards, only the data line 0 is used. The other data lines can be used as independent PIOs.
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:
•
•
•
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 identi-
fies individual cards.
The structure of commands, responses and data blocks is described in the MultiMedia-Card
System Specification Version 2.2. See also Table 66 on page 377.
MultiMediaCard 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 MCCK.
Two types of data transfer commands are defined:
•
•
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.
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.
MCDB0 - MCDB3
MCCDA
MCCDB
MCDA0
MCCK
1
2 3 4 5 6
MMC1
7
SD CARD
1
2 3 4 5 6
MMC2
7
1
2 3 4 5 6
MMC3
1790A–ATARM–11/03
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