at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 593

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

35.7
35.7.1
6384B–ATARM–15-Dec-08
MultiMedia Card Operations
Command - Response Operation
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 identifies
individual cards.
The structure of commands, responses and data blocks is described in the MultiMedia-Card
System Specification. See also
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
MCI Clock.
Two types of data transfer commands are defined:
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
Transfer Operation” on page
The MCI provides a set of registers to perform the entire range of MultiMedia Card operations.
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
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 MultiMediaCard System Specification.
• Command: A command is a token that starts an operation. A command is sent from the host
• Response: A response is a token which is sent from an addressed card or (synchronously)
• Data: Data can be transferred from the card to the host or vice versa. Data is transferred via
• Sequential commands: These commands initiate a continuous data stream. They are
• Block-oriented commands: These commands send a data block succeeded by CRC bits.
either to a single card (addressed command) or to all connected cards (broadcast
command). A command is transferred serially on the CMD line.
from all connected cards to the host as an answer to a previously received command. A
response is transferred serially on the CMD line.
the data line.
terminated only when a stop command follows on the CMD line. This mode reduces the
command overhead to an absolute minimum.
595.).
Table 35-5 on page
AT91SAM9G20 Preliminary
594.
PWSDIV
+ 1 when the bus is inactive.
(See “Data
593