Product manual

SanDisk miniSD Card Product Manual, Rev. 1.0 © 2003 SANDISK CORPORATION 4-1
4. miniSD 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
Command
From
host to
card
Command Response
From
card to
host
Operation (no response)
Operation (no data)
Figure 4-1. “No Response” and “No Data” Operations
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 miniSD Card move in blocks, and 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 data transfers use single or multiple data lines (if the card supports this feature).