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    2021-10-21 17:42:20
    An Overview of SD Card


    Ⅰ Overview
    Ⅱ SD card characteristics
    Ⅲ SD card structure
    Ⅳ SD mode
    Ⅴ SD card derivatives
    Ⅵ SD card specifications

    Ⅰ Overview

    SD memory card is a new generation of high-speed storage devices based on semiconductor fast flash memory. The technology of the SD memory card is derived from the MULTIMEDIA Card format, and it has developed SDIO (SD Input/ Output) card on the basis of a compatible SD memory card. This compatibility includes mechanical, electronic, electricity, signal, and software. SD cards and SDIO cards are usually called SD memory cards.

    The SD card has high memory capacity, fast data transmission rate, great mobile flexibility, and good security, which are widely applied to portable devices, such as digital cameras, tablets, and multimedia players. 

    The SD card structure ensures the security of digital files, and it is also easy to reformat, so there is a wide range of applications. Multimedia files such as music, movies can be easily saved to the SD card. There are many brands of SD cards on the market such as SanDisk, Kingmax, Panasonic, and Kingston. 

    SD card is a new type of storage device with the following features: 

    ● High storage capacity, most common capacity: 8GB, 16GB, 32GB, 128GB, 256GB, etc.

    ● Built-in encryption technology adapts to the copyright protection function based on the SDMI protocol.

    ● High-speed data transfer; maximum read and write rate is 100Mb / s.

    ● Light size, easy to carry, with strong impact resistance.

    Ⅱ SD card characteristics

    The digital copyright protection scheme embedded in the SD card is set according to the Content Protection for Recordable Media (CPRM) proposed in 4C. Its core is the use of the Cryptomeria password (also known as "C2"). This feature is confidential. The DVD-AUDIO CD also uses an encryption scheme that is very similar to CPPM. SD card (Secure Digital Memory Card) is a new generation of memory devices based on semiconductor flash memory. SD card jointly developed its development in Panasonic, Toshiba, and SanDisk in Toshiba and SanDisk in June 1999. The size is like a stamp's SD memory card, with only 2 grams, but has high memory capacity, fast data transmission rate, great mobile flexibility, and good security. 

    The SD card combines SanDisk flash memory card control and MLC (Multilevel Cell) technology and Toshiba 0.16U and 0.13U NAND technology. It is connected to a special drive through a 9-pin interface and does not require an additional power supply to keep the information memorized on it. Moreover, it is an integrated solid medium, there is no moving portion, so there is no need to worry about damage to mechanical movement. 

    The biggest feature of SD cards is to ensure the security confidentiality of data by encryption. The SD card is consistent with the MultiMedia card on the shape and is compatible with the MMC card interface specification. However, some products such as mobile phones, SD cards, and MMS cards cannot be compatible. The SD card is higher than the equivalent MultiMedia Card card in terms of selling. 

    SD card is used for MP3 Walkman, digital camera, digital camera, etc. Its projection area is the same as the MMC card, but the capacity of the SD card is much larger, and the read and write speed is also 4 times faster than the MMC card. At the same time, the interface of the SD card is compatible with the MMC card, supporting the SD card interface to support the MMC card. In 2013, the SD card was rapidly popular in digital cameras, and it became mainstream. The SD card has developed rapidly in 2013 and has begun to threaten the market share of the CF card. This is because the size of the SD card is much smaller than the CF card, and the SD card is getting smaller and smaller in capacity, performance, and price, and the gap between the CF card. The rapid growth of the SD card is definitely not accidental. The most important thing is that the MMC card can also be compatible with SD cards, which is also one of the reasons for SD cards.

    Ⅲ SD card structure

    In addition to the 7 needles of the MMC card, the SD card interface is also added to the two edges, as the data line. 

    In the SD card 3.0 specification, the maximum capacity of the SD card can reach 2TB. The theory's maximum read and write speed can reach 104MB / s (in the latest 4.10 specification, the theoretical maximum read and write speed has increased to 312MB / s). 

    SD card structure

    SD card structure

    The SD card is mainly divided into four parts: external pins, internal registers, interface controllers, and internal storage media. 


    The main pins and functions of the SD card are as follows: 

    CLK: Clock signal, controller, or SD card transmits a command bit or data bit in each clock cycle. The frequency can vary between 0 to 25 MHz in the default speed mode of the SD bus, and the bus manager of the SD card freely produces a frequency of 0 to 25 MHz. In the UHS-I velocity mode, the clock frequency can be up to 208m. 

    CMD: Command and Response Reader, the command is sent by the controller to the SD card, which can be from the controller to a single SD card, or all the cards on the SD bus. The response is the command sent by the memory card Answer, the response can come from a single card or all cards. 

    Dat0 ~ 3: Data cable, data can also be transferred from the controller to the card from the card. 


    The register and its functions are described below: 

    OCR (OPERATING CONDitions Register): 32-bit operating condition register mainly stores the VDD voltage range, and the SD card operating voltage range is 2 ~ 3.6V. 

    CID (CARD Identification Register) Register: The card identification code register, the length is 16 bytes, and the SD card unique identification number is stored. This number cannot be modified after the card manufacturer is programmed. 

    CSD (Card-Specific Data Register) Register: The Carter Data Register contains the necessary configuration information when accessing the card data.

    SCR (SD CARD Configuration Register): SD Card Configuration Register (SCR) provides some special features with the SD card which are 64 bits, and this register content is set by the manufacturer. 

    RCA (Relative Card Address) Register: The card relative address register is a 16-bit writable address register. The controller can select the SD card corresponding to the address by the address.

    DSR (Driver Stage Register) Register: Drive Level Register, which belongs to an optional register for configuring the drive output.  

    Interface controller

    Mainly used to control and manage the core of the internal storage, by receiving the commands sent by the user to control and set, and respond according to the command, and then perform the response data read/write and other operations. 

    Internal storage medium

    Data memory stored Flash block.

    Ⅳ SD mode

    Drive mode

    The SD card has two drive modes: SPI mode and SDIO mode. The interface signals they use are different. In SPI mode, only 4 signal lines of the SD card, ie CS, DI, SCLK and DO (sd card selection, data input, clock, and data output). 

    Transmission mode

    SD card supports three transmission modes: SPI mode (independent sequence input and sequence output), 1-bit SD mode (independent instruction, data channel, unique transmission format), 4-bit SD mode (using the additional pin and certain Reset the pin. Supports four-bit width parallel transmission).

    Low-speed cards typically support 0 to 400 kilobits / second data transfer rates, using SPI and 1-bit SD transmission mode. The high-speed card supports 0 ~ 100 megabits/sec data transmission rate, using 4-bit SD transmission mode; support 0-25 megabits/sec, SPI, and 1-bit SD mode. 

    Manufacturers, vendors, and host adapter manufacturers need to pay SD / SDIO licensing fees, plus $ 1,000 per year to 1,500 US dollars. However, the SDIO card and MMC adapter manufacturers do not have to authorize fees. The MMC card uses a 7-pin interface, the SD card, and the SDIO card use a 9-pin interface.

    Ⅴ SD card derivatives

    MINI SD card

    MINI SD was developed by Panasonic and SanDisk. The first appearance was in the SanDisk booth in the 2003 CEBIT exhibition. Since then it has added Memory Stick Duo and XD cards such as a small memory card specification. 

    The design of the MiniSD card is initially made to take pictures with a photo pine mobile phone. 

    It can also be used as a general SD card by the SD adapter card. 

    The capacity of the MiniSD card is from 16MB to 8GB, while the capacity of the MiniSDHC card is from 4GB to 16GB. 

    sizes of different SD card

    sizes of different SD card

    Micro SD card

    On the ultra-small memory card product, the SD Association took the lead in incorporating T-Flash into its family and named Micro SD to replace the status of Mini SD.

    Only after the nail size Micro SD has been amazed after the launch of 2005. In 2008, the phone has spread this very small memory card. 

    M2, Micro SD, and MMC Micro are listed in the world's smallest mini memory card, and the ultra-small volume has a greater advantage. It can be applied to various types of digital products. For exquisite digital life, it has also played the role of "promoting wave". It is unfortunately only MICRO SD that only survives. The M2 card is a Sony version of Micro SD, eventually replaced by Micro SD. 

    Ⅵ SD card specifications

    Rate level

    "X" representation (SD1.0 specification, not used now):

    It is calculated from the 150kb / s of the CD-ROM to a 1-fold speed calculation method. Basically, they can be 6 times faster than the standard CD-ROM (900 kB/sec), while the high-speed SD card can transmit 66X (10 MB / sec) and 133x or higher speed. Some digital cameras require high-speed SD cards to shoot more smoothly, and continuous shooting photos more quickly.

    Up to December 2005, most of the equipment followed from the SD card 1.01 specification, and the higher speed to 133X equipment also followed from 1.1 specifications, up to 12.5MB / sec.

    SD2.0 specification:

    The rate of ordinary cards and high-speed cars is defined as class2, class4, clas6, and class 10 levels. Before the Class 10 card, there is a card that has Class11 and Class13, but this standard is eventually not a consensus with the SDA. 

    SD3.01 specification:

    Also known as the ultra-high-speed card, the rate is defined as UHS-I and UHS-II. By the second quarter of 2013, only the UHS-I card has been listed. UHS-II was released in the fourth quarter of 2012, but in terms of technology development before 2014, UHS-I was complete enough to spend 2014 or even longer. The speed level of the UHS-I card is divided into UHS-Class0 and UHS-Class1. The Class and SD2.0 of the UHS-i are different, and there is no clear Class0 card, and the literal meaning is the card that does not reach Class1. It may be summarized as Class0 in the future. Class1 represents the maximum read of 104MB / s, while the Class represents the SD2.0 standard represents the smallest speed range.

    The marker symbol on the card is shown in Figure.

    Rate level symbol on the card

    Different levels of reading speed and application requirements that meet:

    Different levels of reading speed and application requirements

    Capacity level

    The SD card capacity is currently three levels, that is, SD, SDHC, and SDXC. 

    The table below is the level capacity range and standard disk format:

    Level capacity range and standard disk format

    The SD capacity is 8MB, 16MB, 32MB, 64MB, 128MB, 256MB, 512MB, 1GB, 2GB.

    The SDHC capacity has 2GB, 4GB, 8GB, 16GB, 32GB.

    The SDXC capacity has 32GB, 48GB, 64GB, 128GB, 256GB, 512GB, 1TB, 2TB.

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