MicroSD Card

10 June 2018 - 0 Comments

MicroSD Card

MicroSD Card Pinout

Pin Configuration

Pin Number	Pin Name	In SD Mode	In SPI Mode
1	DAT2/X	有限公司nnector Data line 2	No use
2	DAT3/CS	有限公司nnector Data line 3	Chip Select
3	CMD/DI	有限公司mmand / Response Line	Data Input
4	VDD/VDD	Power supply (+3.3V)	Power supply (+3.3V)
5	CLK/SCLK	Clock	Serial Clock
6	VSS/VSS	地面	地面
7	DAT0/D0	有限公司nnector Data line 0	Data Out
8	dat1/x	有限公司nnector Data line 1	No use

MicroSD Card Features and Specifications

Operating Voltage: 2.7V to 3.3V
Capacity: 4GB, 8GB, 16GB, 32GB etc..
File System: SD/SDHC/SDXC
存储系统：FAT12和FAT16
Transfer Speed: 95 Megabytes per second (typically)
Speed Class: Class 2 to Class 10
Form Factor: 11mm × 15mm × 1mm

Where to use an SD card

SD Cards are the most commonly used存储设备inembedded applications. Almost all microcontrollers have a limited Flash memory for programming and a limited EEPROM memory to store important data. However for projects involving Data logging or Pictures or other heavy graphics the programmer might have to save huge piece of data in terms of Mega bytes. In that situation an SD card is employed.

How to use an SD card

The terms SD card stands for “Secure Digital” Card, there aremany types of SD cardsstarting from the RS-MMC big sized ones used in cameras to the micro and mini SD cards that are commonly used in mobile phones, MP3 players etc. Although there are few important differences between all these cards, the underlying working principle is all the same.

SD卡可以以两种操作模式工作，一种正在使用SD modecommands and the other isSPI mode. Most of the Digital cameras and mobile phones will use the SD mode to communicate with the SD card, however this is not of our interest because only the SPI mode to communicate between an SD card and a Microcontroller likeArduino(ATmel),PIC,AVR, etc.. Asimple connection diagram for SPI with a microcontroller如下所示：

micro SD card Microcontroller Communication in SPI mode

The SPI communication requires only four wires and is vastly supported by most of the microcontrollers. However the SD card operates with a voltage of 3.3V and all its pins speak with only 3.3V, the Microcontroller on the other hand might work with +5V in those cases a bi-directional logic level shifter (like74HC245) that can convert the 5V signals to 3.3V is recommended. Once you have interfaced the Card you would have to initialize it and then start communicating with it through the SPI commands, it is not possible to cover the entire process here so you can read through the datasheet below to get more info.