AT83SND2CMP3 datasheet(52/97 Pages) ATMEL

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AT83SND2CMP3

7524B–MP3–05/06

Bus Lines

The MultiMedia Card bus architecture requires all cards to be connected to the same set

of lines. No card has an individual connection to the host or other devices, which

reduces the connection costs of the MultiMedia Card system.

The bus lines can be divided into three groups:

•

Power supply: V

SS1 and VSS2, VDD – used to supply the cards.

•

Data transfer: MCMD, MDAT – used for bi-directional communication.

•

Clock: MCLK – used to synchronize data transfer across the bus.

Bus Protocol

After a power-on reset, the host must initialize the cards 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 which starts an operation. A command is

transferred serially from the host to the card on the MCMD line.

•

Response: a response is a token which is sent from an addressed card (or all

connected cards) to the host as an answer to a previously received command. It is

transferred serially on the MCMD line.

•

Data: data can be transferred from the card to the host or vice-versa. Data is

transferred serially on the MDAT line.

Card addressing is implemented using a session address assigned during the initializa-

tion phase, by the bus controller to all currently connected cards. Individual cards are

identified by their CID number. This method requires that every card will have an unique

CID number. To ensure uniqueness of CIDs the CID register contains 24 bits (MID and

OID fields) which are defined by the MMCA. Every card manufacturers is required to

apply for an unique MID (and optionally OID) number.

MultiMedia Card bus data transfers are composed of these tokens. One data transfer is

a bus operation. 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 MDAT

and the MCMD lines are transferred synchronous to the host clock.

2 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 MCMD 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 MCMD line similarly to the stream read.

Figure 37 through Figure 41 show the different types of operations, on these figures,

grayed tokens are from host to card(s) while white tokens are from card(s) to host.

Figure 37.

Sequential Read Operation

Data Stream

Command

Response

MCMD

MDAT

Data Stop Operation

Data Transfer Operation

Command

Response

Stop Command

AT83SND2CMP3 Datasheet(PDF) 52 Page - ATMEL Corporation

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