SanDisk SDSDB-32-201-80 - Industrial Grade Flash Memory Card Manual download pdf (Page 53)

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

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/from the Industrial Grade 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).

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SanDisk SDSDB-32-201-80 - Industrial Grade Flash Memory Card Manual Page 53