Sd Card Protocol Description; Sd Bus Protocol - SanDisk SDSDB-016G-A11 Product Manual

Revision 2.2
4

SD Card Protocol Description

4.1

SD Bus Protocol

Communication over the SD bus is based on command and data bit streams, which are
initiated by a start bit and terminated, by a stop bit:
Command—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—token that 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 lines.
Figure 4-1
From host
to card(s)
CMD
DAT
Card addressing is implemented using a session address that is assigned to the card during
the initialization phase. The basic transaction on the SD bus is the command/response
transaction (see Figure 4-1). This type of bus transaction transfers their information directly
within the command or response structure. In addition, some operations have a data token.
Data transfers to and from the SD Card are done in blocks. CRC bits always follow data
blocks. Single and multiple block operations are defined. Note that the Multiple Block
Operation mode is better for faster write operation. A multiple block transmission is
terminated when a stop command follows on the CMD line. The host can configure a data
transfer to use single or multiple data lines (provided the card supports this feature).
© 2004 SanDisk Corporation
"No Response" and "No Data" Operations
From host
to card
Command
Operation (no response)
4-1
Chapter 4 – SD Card Protocol Description
SanDisk SD Card Product Manual
Command
Response
Operation (no data)
From card
to host
12/08/04