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Nations Technologies Inc.
Tel
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+86-755-86309900
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Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
SDIO bus topology
Communication on the SDIO bus is achieved by transferring commands and data. After power-on reset, the host must
initialize the card through a special message-based bus protocol. Each message is a command/response structure,
additionally, some messages have data tokens. Each part of the message is described in detail as follows:
Command: The command is serially transmitted on the CMD line and is a token to initiate an operation, sent
from the host to the card
Response: A response is serially transmitted on the CMD line, sent from the card to the host in response to a
previously received command.
Data: Data is transmitted through the data line. Data can be transferred from the card to the host or from the host
to the card. The number of data lines used for data transfer can be 1 (SDIO_DAT0), 4 (SDIO_DAT[3:0]) or 8
(SDIO_DAT[7:0]).
The structure of commands, responses and data blocks is described in the card functional description chapter. A data
transfer is a bus operation. A normal operation always consists of a command and response. Additionally, some
operations have a data token. There are other operations that include their information directly in the command or
response structure. In this case, the operation has no data token.
There are two types of data transfer commands: block and stream. Data transmitted on SD/SDIO memory cards and
CE-ATA devices is transmitted in the form of data blocks; data transmitted on MMC is transmitted in the form of
data blocks or data streams;
Data streams and data block transfers are defined as follows:
Data flow: The command initiates a continuous data flow, and the data transmission is terminated only when a
stop command appears on the CMD signal line. This mode minimizes command overhead (only MMC is
supported).
Data block: The command successfully sends a data block followed by a CRC check. Read and write operations
allow single or multiple block transfers. As with continuous read, a multi-block transfer is terminated when a
stop command appears on the CMD signal line.
The basic operations on the SDIO bus are command/response operations, and this type of bus transaction passes their
information directly in a command or response structure. In addition, some operations have data tokens. Data transfer
between the card and the device is done through blocks. Each transmission type is shown in the following figure:
