know your sd memory card

7/29/2019 Know your SD Memory Card

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Know your: SD Card

SD, sound weird; what is SD as we know its memory device, it expanse as secure

digital (SD).Its basically used in PDA device, Mobile device, GPS device, and many more. SD

comes in different memory size, about 2 GB to 128 GB even more. The SD card comes with

three specifications Standard, Mini, and Micro. SD card specifications are maintained by six

hundred members association. Mini SD and Micro SD come with adapter support.

Standard SD vs Micro SD

Standard SD Micro Sd

Dimension 32 x 24 x2.1 mm 21.5 x 20 x 1.4mm

Card Weight 2.0 grams 1.0 grams

Operating Voltage 2.7-3.6V 2.7-3.6V

Write Protect Yes Yes

Pins 9 11

Interface SD or SPI SD or SPI

Current Consumption


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Pin Layout:

Standard SD card Pin Layout

Sno Name SD Description

1 CD/DAT3/CS Data line 3

2 CMD/Datain Command/response

3 VSS Supply ground

4 VDD Supply voltage

5 CLK Clock

6 VSS2 Supply Voltage Ground

7 DAT0 Data line 0

8 DAT1 Data line 1

9 DAT2 Data line 2

SPI- Serial Peripheral Interface

The SPI (Serial Peripheral Interface) bus is a synchronous serial bus standard named by

Motorola that operates in full duplex mode. Devices on a SPI bus operate in master slave

mode, where the master device initiates the data transfer, selects a slave, and provides a

clock for the slaves. This protocol used to interface SD card to microcontroller, this protocol

used in following,

SD

1 2 3 4 5 6 7 89


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Memory devices (SD cards) Sensors Real-time clocks Communications devices Displays

Reading Data

The SD card in SPI mode supports single-block and multiple-block read operations. The host

should set the block length. After a valid read command the card responds with a response

token, followed by a data block and a CRC check. The block length can be between 1 and

512 bytes. The starting address can be any valid address in the address range of the card. In

multiple-block read operations, the card sends data blocks with each block having its own

CRC check attached to the end of the block.

Writing Data

The SD card in SPI mode supports single- or multiple-block write operations. After receiving

a valid write command from the host, the card responds with a response token and waits to

receive a data block. A one-byte start block token is added to the beginning of every data

block. After receiving the data block the card responds with a data response token, and

the card is programmed as long as the data block is received with no errors. In multiple-

block write operations the host sends the data blocks one after the other, each preceded by

a start block token. The card sends a response byte after receiving each data block. Card

Size Parameters SD cards are available in various sizes. At the time of writing, SanDisk

Corporation (www.sandisk.com) offered the models and capacities. The company may now

be offering models with 4GB or even greater capacity. In addition to the normal storage

area on the card, there is also a protected area pertaining to the secured copyright

management. This area can be used by applications to save security-related data and can be

accessed by the host using secured read/write commands. The card write protection

mechanism does not affect this area. the size of the protected area and the data area

available to the user for reading and writing data. For example, a 1GB card has 20,480

blocks (one block is 512 bytes) of protected area and 1,983,744 blocks of user data area.

Model Protected Area User Area

SDSDB-16 352 28,800

SDSDB-32 736 59,776

SDSDJ-64 1376 121,856

SDSDJ-128 2624 246,016

SDSDJ-256 5376 494,080

SDSDJ-1024 20,480 1,983,744


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1 Block = 512 bytes

Data can be written to or read from any sector of the card using raw sector access methods.

In general, SD card data is structured as a file system and two DOS-formatted partitions are

placed on the card: the user area and the security protected area. The size of each area is

shown in Table 7.7. For example, in a 1GB card, the size of the security protected area is 519

sectors (1 sector is 512 bytes), and the size of the user data area is 1,982,976 sectors.

Card Holder

A card can be inserted and removed from the bus without any damage. This is because all

data transfer operations are protected by cyclic redundancy check (CRC) codes, and any bit

changes caused by inserting or removing a card can easily be detected. SD cards typically

operate with a supply voltage of 2.7V. The maximum allowed power supply voltage is 3.6V.If the card is to be operated from a standard 5.0V supply, a voltage regulator should be used

to drop the voltage to 2.7V. Using an SD card requires the card to be inserted into a special

card holder with external contacts so connections are easily made to the required card pins.

know your sd memory card

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