Secure Digital (Sd) Card Protocol Description; Sd Bus Protocol - SanDisk SDSDB-32-201-80 - Industrial Grade Flash Memory Card Product Manual

4. Secure Digital (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—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 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.
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/from the SD Card are done in blocks. Data blocks are always followed by CRC bits. 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. Data
transfer can be configured by the host to use single or multiple data lines (as long as the card supports this feature).
SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION
From
host to
card
Command
Operation (no response)
Figure 4-1. "No Response" and "No Data" Operations
Command Response
Operation (no data)
From
card to
host
4-1