SD Card is one of the important memories used in Embedded systems. This is a type of NAND Flash and is a Non-Volatile Memory. SD Cards have the good advantages of low size, sufficient endurance and provide easy to update option. Standard variants of SD Card include SD, micro SD, SDXC, SDHC, SDUC. Following is the pin out of the micro SD Card which interface to the Processor or a Microcontroller.
1. Check out the pin out of Microcontroller or Processor and connect the corresponding pin of SD card.
2. Either it be reducing power dissipation or prolonging the life of SD card, the CARD power can be controlled using a MOSFET circuitry. A Simple P-Channel MOSFET can be used for the control.
Some designs have auto-wake up conditions which add additional controls to the base of the MOSFET.
3. SD Specification 6.0 includes Low Voltage Signaling memory card (LVS) that may support either 3.3V or 1.8V signaling, accordingly, level translator need to be introduced between SD card and processor
4. The SD card can be used in SD mode or SPI mode, the pin out in SPI mode vary from SD Mode. The host which is processor or Microcontroller has to select the mode of oepration.
5. Below is how the pin assignment looks like in SD Card. This is from Kingston SD Card and check corresponding datasheet of SD card you are using in design to interface.
7. Normally, in our applications, where there is no restriction on the speed, SD clock speed of 25 MHz is used. Any clock frequency beyond and high speeds useUHS-I, UHS-II Ultra High Speed (UHS) bus which is available on some SDHC and SDXC cards UHS has versions UHS-I, UHS-II and UHS-III. UHS-III can be used up to 624MB/s.The speed class is indicated on the SD card. For example, in the below image '3' indicates speed class and 'I' indicates Bus Speed.
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