Atmel SAM9X25, Manual

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11054A–ATARM–27-Jul-11
SAM9X25
Figure 34-6. SD Card Bus Connections with One Slot
Note: When several HSMCI (x HSMCI) are embedded in a product, MCCK refers to HSMCIx_CK,
MCCDA to HSMCIx_CDA MCDAy to HSMCIx_DAy.
When the HSMCI is configured to operate with SD memory cards, the width of the data bus can
be selected in the HSMCI_SDCR register. Clearing the SDCBUS bit in this register means that
the width is one bit; setting it means that the width is four bits. In the case of High Speed Multi-
Media cards, only the data line 0 is used. The other data lines can be used as independent
PIOs.
34.8 High Speed MultiMediaCard Operations
After a power-on reset, the cards are initialized by a special message-based High Speed Multi-
MediaCard 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 High Speed MultiMe-
dia-Card System Specification. See also
Table 34-6 on page 610 .
High Speed 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 infor-
mation 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
HSMCI 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.
2345
6
17
MCDA0 - MCDA3
MCCDA
MCCK
8
SD CARD
9