SD bus protocol

SD bus protocol

SD bus communication is based on commands and data bit streams. The Start and Stop bits end. SD bus communication has three elements:

Command: the host sends the command to the card device and uses the cmd line to send the command;

Response: sends data from the card end to the host end. as a response to the previous cmd, the data is sent through the Cmd Line;

Data: transmits data from the host to the card, from the card to the host, and through the data line.

 

Commands

There are four command types used for the control card device. Each Command has a fixed length of 48 bits:

1. Broadcast commands (BC), no response: broadcast-type command, no response is required;

2. Broadcast commands with response (wb): broadcast-type command and response required;

3. addressed (point-to-point) commands (AC): The host sends data to the specified card device without data transmission;

4. Address (point-to-point) Data transfercommands (adtc): The host sends data to the specified card device with data transmission.

Command Format:

 

Card register

Several major registers: OCR, CID, CSD, RCA, and SCR.

Operation Condition register (OCR): 32-bit OCR includes a working voltmeter supported by the card device;

Card identification number register (CID): contains the card information used in the card recognition phase, including the manufacturer ID and product name;

Card specific data register (CSD): the CSD register provides information on how to access the card device, including defining the data format, error verification type, maximum access times, and data transmission rate;

Relative card Address Register (RCA): The relative address allocated during card recognition. The default relative address is 0000 h;

SD card configuration register (SCR): SCR is a configuration register used to configure the special features of SD memory card.

 

Response

All response are sent to the host through the cmd line. The R4 and R5 response types are unique in sdio:

1. R1 (normal response command): used to respond to common commands;

2. R2 (CID, CSD register): used to respond to cmd2, limit 10, or limit 9, and uses the CID or CSD register as the response data;

3. R3 (OCR register): used to respond to the acmd41 command and use the OCR register as the response data;

4. R6 (published RCA response): assigns a response to the address of the relative card;

5. R7 (card interface condition): returns the voltage information supported by the card in response to limit 8;

6. R4 (Release 5): responds to Issue 5 and uses the OCR register as the response data;

7. R5 (Limit 52): Limit 52 is a read/write register instruction, and R5 is used for the response of limit 52;

Response format:

* ** For details, refer to spec ***