Introduction to SD/MMC registers

Familiar with SD/MMC-related registers, which can assist in understanding the protocols. So this article will introduce the SD/MMC-related registers?

1. SD card internal architecture

Before getting familiar with SD/MMC registers, let's take a look at the internal architecture of the SD card, as shown in:

2. Introduction to SD/MMC registers

We can conclude that the SD card contains seven internal registers.

I. OCR, CID, CSD, and SCR registers Save the configuration information of the card;

2. The RCA register stores the address temporarily allocated by the card during communication (only applicable to SD mode );

III. The CSR register card status and SSR register SD status Save the card status (for example, whether the write is successful, check whether the CRC of the communication is correct). The content of these two registers is related to the communication mode (SD mode or SPI mode.

4. The mmccard does not have the SCR and SSR registers.

The following describes the important registers in seven registers, namely, CID, CSD, Scr, OCR, and RCA.

2.1. Card identification register (CID)

The Cid register is 16 bytes long, as shown in the following table. It contains the special identifier (ID) of the current card ). This information is programmed (burned) during the production of the card, and the master controller cannot modify their content. Note: The CID register of the SD card and the CID register of the MMC card are different in the record structure.

2.2.card specific data register (CSD)

The description data register (CSD) is 128 bytes long, as shown in the following table. This card contains the necessary configuration information for accessing the card data. The "cell type" column defines that the CSD areas are read-only (R), one-time programming (R/W), or erasable (R/W/E) ["r/W" means that data can be erased multiple times. "R/W (1)" means data can be written only once and cannot be erased]. The values displayed in this table correspond to the respective regions and codes in the actual CSD structure. The style of the CSD area is based on the column tag (and a check mark √. Note that the CSD registers in the SD card and the CSD registers in the multimedia card have different structures.

In sd3.0, CSD is divided into version 1.0 and Version 2.0. Version 1.0 corresponds to SD cards of standard capacity, and Version 2.0 corresponds to SD cards of high capacity and ultra high capacity.

The CSD version 2.0 is as follows:

2.3.sd card configuration register (SCR)

In addition to the CSD register, there is also a configuration register name: SD card configuration register (SCR ). SCR provides some special features of the SD card in this card. It is 64-bit in size. The register content is set by the manufacturer in the production plant, and the mmccard does not have SCR.

Scr_structureThe version number of the SCR structure in the physical level description of the SD card.

Sd_specDescribes the description version supported by this SD card on the physical level.

Data_stat_after_eraseDefines the status of the erased data. Is either "0" or "1" (the vendor that depends on the card ).

Sd_securityDescribes the security algorithms supported by the card. 0: None 1: Security Protocol 1.0 Security description version 0.96 2: Security Protocol 2.0 Security description version 1.0-1.01. Other Reserved

Sd_bus_widthsThe width of all data bus supported by the card. Starting from the two bus modes that the SD card supports at least one or four bits in width, any SD card will have at least two bits (I .e., sd_bus_width = 0101 ), 1.4 bits are retained.

2.4.operating conditions register (OCR)

This 32-bit working condition register stores the card's VDD voltage profile. Any standard SD card master controller can use 2 V to 3.6 V operating voltage to enable the SD card to perform this voltage recognition operation (cmd1 ). In any case, the array operation that accesses the storage requires an operating voltage of 2.7 V to 3.6 V. The OCR registers display the voltage range required for accessing card data. OCR register structure description:

2.5.rca register
The 16-bit card address register stores the device addresses that are released during card recognition. This address is used by the host to communicate with the card after the card is identified. This register is valid only in SD bus mode.