table of Contents
01, SD card
SD card is the English abbreviation of SecureDigitalCard, literally translated as "Secure Digital Card", formally abbreviated as SD, is a proprietary non-volatile memory card format developed by the SD Association for portable devices. Because of its small size, fast data transmission speed, hot-swappable and other excellent characteristics, it is widely used in portable devices.
This standard was launched by SanDisk, Matsushita Electric and Toshiba in August 1999. As an improvement to MultiMediaCard (MMC), it has now become an industry standard. These three companies form SD-3C, LLC, which licenses and executes intellectual property rights related to SD memory cards and SD hosts and auxiliary products.
The two companies also established the non-profit organization SD Association (SDA) in January 2000 to promote and create SD card standards. SDA now has approximately 1,000 member companies. SDA uses multiple trademark logos owned and licensed by SD-3C to enforce compliance with its specifications and ensure user compatibility.
SD card capacity
SecureDigital includes five card series available in three different sizes. These five series are the original standard capacity (SDSC), large capacity (SDHC), extended capacity (SDXC), super capacity (SDUC) and SDIO, which combine input/output functions with data storage. The three form factors mentioned are original size, micro size, and micro size.
SD card appearance
Drive mode
SD card has two drive modes: SPI mode and SDIO mode. The interface signals they use are different. In SPI mode, only the 4 signal lines of the SD card are used, namely CS, DI, SCLK and DO (respectively the chip select, data input, clock and data output of the SD card).
Transmission mode
SD card supports three transmission modes: SPI mode (independent sequence input and sequence output), 1-bit SD mode (independent command and data channel, unique transmission format), 4-bit SD mode (using additional pins and some Reset pins. Supports four-bit wide parallel transmission).
The pin definitions of the three modes of SD card:
The internal structure and pins of the SD card are shown in the figure below:
Overwrite protection switch
There is usually a switch on the right side of the SD card, which is the overwrite protection switch. When the overwrite protection switch is turned off, the SD card will be overwritten and the data can only be read. When the overwrite protection switch is in the upper position, data can be overwritten. Since this protection switch is optional, some brands of SD cards do not have this protection switch.
Schematic diagram
Although the standard SD card is nine pins, the schematic diagram is that the SD card holder is not an SD card! ! , So the schematic diagram is generally 11 feet or more.
Generally, pin 10 is to detect whether the card is inserted, pin 11 is to detect the write protection of the card, and there are other pins that are used to fix the card holder. In fact, you can simply use these two pins. This is why SD The number of pins is different for different pin versions in the card schematic.
Typical circuit connection
SDIO connection mode
SPI connection mode
02, TF card
Micro SD Card, formerly known as Trans-flashCard (TF card), was officially renamed MicroSD Card in 2004 and was invented by SanDisk. MicroSD card is a very small flash memory card whose format originated from the creation of SanDisk. Originally, this memory card was called T-Flash, and later renamed TransFlash. The reason for the renamed MicroSD is that it was renamed as MicroSD because of the SD Association ( SDA) Adopted.
Its size is 15mm x 11mm x 1mm, which is almost the size of a fingernail, and it is the smallest memory card currently available. It can also be connected to the SD card slot through an SD adapter card. At present, MicroSD cards provide 128MB, 256MB, 512MB, 1G, 2G, 4G, 8G, 16G, 32G, 64G, 128G capacities (During the MWC2014 World Mobile Communications Conference, SanDisk broke the tradition of memory cards with a maximum capacity of 64GB. A Micro SD XC memory card with a capacity of up to 128GB was officially released.
MicroSD is smaller in size and can be converted to SD card. The circuit and pins of TF card are the same as that of SD card.
PCB package of TF card
As can be seen from the figure below, the pin near the circle is not connected to TF.
So do TF package and circuit, and pin 9 is left floating
03, TF to SD card
TF card can be used as SD card after SD card converter.
Internal circuit
04, matters needing attention
TF card + card holder, the combination can also be used as SD card, but a large part of TF card does not support SPI access mode, so when SPI drives SD card, choose a large card (SD card) as much as possible, don’t choose TF card.