Saturday, January 31, 2009

SD/SDHC Card Interfacing with ATmega8 /32 (FAT32 implementation)

Hi friends,
Here is my project on interfacing of SD Card (microSD). microSD cards are available very cheap nowadays, a great option for having a huge memory in any embedded system project. It is compatible with SPI bus, so the interfacing is easy. SD card adapters are also easily available in market, one can easily make a bread-board adapter by soldering few pins on it. Following figures show the SD card pin-out & the bread-board adapter design by soldering 7-pins of a breakout header on the microSD adapter (Click on images for larger view).

I had started this project with 1GB microSD card from SanDisk (later on tested with transcend cards also). The microcontroller is AVR ATmega8 or ATmega32 running at 8Mhz internal clock. MAX232 is used to interface the circuit with PC for monitoring the data. A 3.3v supply is used for powering the mega8, microSD and max232 (though the specified supply for max232 is 5v, it works comfortably at 3.3v).7 pins of the microSD are used here, shown in the figure of pin-out.

Schematic for ATmega8 is shown here (updated on 10 May 2010, SD series resistors are removed, as they were limiting the speed of SPI bus. 51k pullups are added on CMD/DAT lines. This gives better stability with different cards. Also, two 3.6v zeners are added to protect SD in case when the ISP programmer voltage levels are of 5v. these diodes are not required if your programmer has settings for 3.3v output)
(Note: VCC & GND pins of MAX232 are not shown in the schematic, but they must be connected in the actual hardware)
Following is the schematic for ATmega32, without RTC (updated on 10 May 2010):

Following is the schematic for ATmega32, with RTC (added on
17 May 2010; CS pin correction, PB4 instead of PB1, done in Mar 2014). Here two supply voltages are used, 3.3v for SD & 5v for remaining ICs.

The aim of this project was to learn interfacing of SD card and to understand the data transfer in raw format as well as in FAT32 format. I started with raw data transfer, sending some data to any block of the microSD, reading a block of it, reading and writing multiple blocks, erasing multiple blocks. All this in raw format. I used RS232 for viewing the data read by microcontroller from SD card. The uc sends the data to HyperTerminal. Similarly, to write data to card, the data was fed thru HyperTerminal, by typing some text.

Once raw data transfer achieved, I formatted the card with windowsXP (FAT32) and loaded it with some text files, directories and other files (all stored in root directory of the card). After that I wrote the FAT32 routines to read files, get file list (using HyperTerminal again), finding the total/free memory of card. All this data is sent to HyperTerminal by the uc.

Following is the HyperTerminal window showing different options:
Options 0 to 4 are low level functions dealing with raw data. If you use option 0, 1 or 3, you may have to reformat the card before using the FAT32 routines.
0: Erases selected number of blocks strating from selected block
1: Writes data to specified SD block address. Data to be entered in HyperTerminal using PC keyboard
2: Readss data of specified SD block address. Data is displayed on HyperTerminal window
3. Writes selected number of blocks strating from selected block
4. Reads selected number of blocks strating from selected block

Here, the multiple-block functions related to options 3 & 4 are disabled due to memory constraint as that time mega8 was used for testing and these functions are not required for FAT32 testing. While testing with mega32, options 3 & 4 can be enabled by removing a macro (#define FAT_TESTING_ONLY) defined in SD_routines.h.

Options 5 to 9 are related to FAT32 . Only short file names are supported right now, 8byte name+3bytes extension. If you store a long name file in SD, it will be displayed by these routines in short name format only.
For testing these options, format the card with FAT32 file system and store some directories and text files (because text files can be read & checked thru HyperTerminal).

5: Displays list of available directories and files with size (in the root directory of the card)
6: Reads a specified file and displays the file contents on HyperTerminal
7: Create/Append file with specified name, enter text from HyperTerminal
8: Deletes any existing file with specified name
9: Displays total & free memory of the card (using FSinfo sector of the SD card)

Following figures show the HyperTerminal window when options 5 & 9 are selected:
(These figures show menu from Ver2.3 or earlier. Menu style is changed from Ver_2.4 onwards, which is shown in the update history)

Note: HyperTerminal is used here at 19200 baudrate, No parity, Flow Control 'none'.

This project needs very few components and can be done easily at home. Try it out!

Download the source code files from here
Download here the zipped source code files modified for mega32, written in winAVR-AVRStudio.

Version 2.4.1 (RTC added for Date/Time entries) 17 May 2010/24 Apr 2011
Version 2.3 (SDHC support added) 09 May 2010
Version 2.2 (No SDHC support) 13 Sep 2009

Download EAGLE schematic file of Ver 2.4

Download/view source code files V2.1 (for ATmega8):
Following files are compiled using winAVR inside AVRStudio. This Version does not support SDHC cards. Also, append file feature is not available.
1. SD_main.c
2. SD_routines.c & SD_routines.h
3. FAT32.c & FAT32.h (Ver 2.1, last updated-13 Sep 09)
4. SPI_routines.c & SPI_routines.h
5. UART_routines.c & UART_routines.h
6. Makefile
7. HEX file (Ver 2.1, last updated-13 Sep 09)

Please put up a comment or mail me if you find a bug in the code. The updates are because of valuable suggestions & comments from the users of this code. Thanks a lot!!

Buy from Farnell (Element14): ATmega32 (India), ATmega32 (USA)

Related posts:
You can visit my post of microSD ATmega32 Data-Logger, which uses modified FAT32 library for automatically creating files without using hyper terminal.
If you want to test FAT32 functions or learn more without making the microcontroller hardware, you can visit my post here: microSD-FAT32 using Visual C++)

Update History-----------------------------------------------------------------------------
Version 2.4:

- Real Time Clock circuit support is added for time & date entries in the files. Now the current date of file creation and file update will be entered in the FAT table (can be viewed by checking file 'properties' using a PC)
(The RTC will also be useful in data-logging with time-stamp)
- Three more options added in the Hyper Terminal menu for displaying or updating RTC date & time. New menu is shown in the above figure.

Ver 2.4.1:
- Same as 2.4, with a bug fix for RTC: 'twi_init' function added to define I2C clock freq. 100K@ 16MHz (50k@8MHz). This was taking default values earlier, which was as high as 500K@8MHz, not desirable

(Note: Version 2.2, 2.3 & 2.4 are tested on ATmega32, but they can be adopted to any controller having RAM >= 1KB and Flash >= 16KB)
Current memory usage (Ver_2.4): Flash: 12908 Bytes; RAM: 700 Bytes (appx.);

Version 2.3:
- Support for SDHC cards added (tested with SanDisk & Transcend microSD and microSDHC cards). The initialization sequence and command formats are modified.
- A bug which was causing the program flow to go into infinite loop if the character number 512 in a sector was a CR (Carriage Return, '\r'), in the writeFile function. Thanks to David & Piotr M. who pointed it out in the comments.
- Code is also tested successfully at 16MHz clock (8MHz SPI clock) with for SD/SDHC cards.

Follwing are the Hyper Terminal windows showing card detection (One window shows baudrate as 38400, that was while testing for higher clock speeds, current code still uses 19200 baud and 8MHz internal clock of Mega32).

Version 2.2:
- Append file feature added. 'createFile' function replaced with writeFile, which looks for the filename first, if the given file name doesn't exist then it creates new file and writes data, but if the file already exists, then it opens it and appends the entered data.
- A bug removed which was giving error related to use of 'LONG'
- The FAT32.c & .h files are updated on 13 Sep 09 to remove a bug which was limiting file size to 32MB (Thanks to Kun-Szabo Marton who pointed it out)

Data transfer rate: 1 raw data block (512 bytes) takes 4.15ms for reading or writing (123.37 KBytes/s) at current 4 MHz SPI clock rate. If you have flash more than 8k, you can declare the SPI_receive() and SPI_transmit() functions as 'inline' functions. This will increase the transfer rate to 140 KBytes/s. These transfer rates can be further increased by using a 16MHz crystal (8 MHz SPI clock). FAT32 file reading is done at 78 to 91 KBytes/sec.

Version 2.1:
- A bug removed which stopped creating new files after 32*8 files in the root directory
- The root directory was unnecessarily getting expanded by one cluster whenever a file was created. Fixed in the new version
- Also, the fixed cluster size of 8 sectors is removed, this version will support other cluster sizes as well

Version 2.0:
- Support added for SD cards having first sector as MBR rather than the boot sector
- createFile and deleteFile functions added
- A bug fixed in reading files stord at far locations in memory also correction made to accept 8+3 char file name (by mistake, it was taking 7+3 earlier)
- FSinfo sector used for storing total free cluster count &
next free cluster number for faster file access
- Instant freeMemory display (earlier it was taking more than 30secs) using FSinfo sector. FSinfo sector is updated now whenever a file is created or deleted
- File memory size display in decimal, like windows (earlier it was in hex)
- Raw SD functions multiple block read and write, which are not required for FAT32, are disabled using FAT32_TESTING_ONLY macro for getting extra space required by createFile & deleteFile changes (you can activate it if you have more than 8k flash) Right now flash is 99.9% full
- Clock speed raised from 1Mhz to 8 MHz, new SPI speed (after SD initialization): 4MHz instead of 500K & baudrate: 19200 (for HyperTerminal) instead of 4800

1. Microsoft's FAT32 specification document
2. SanDisk SD mnual v1.9
3. SD-Simplified Physical Layer Spec. Ver 4.10
4. F. Foust's Application Note on SD
5. FAT32 Structure info, includes MBR details
6. Simple FAT32 Structure explanation
7. Chan's FAT library
8. SD Association's Website for further info



«Oldest   ‹Older   601 – 670 of 670
Asif said...

Hi MR Dharmanitech,

I hope my Email find you all the best in your health.
I have two questions regarding FAT32 library,

Does this library support to create folders ?
Does this library support long file name support(Currently only 8 characters)?

I shall be very thankful for your quick reply.

Thanking you in anticipation


Asif said...

If these two features are not supported, how can we update the library to support these features.

Hartley Thanks for your co-corporation in this regards

Anonymous said...

Surely one of the best project in the web :) Thank you very much for your project

Vasile Guta Ciucur said...

Well that is simple. The key is... CS (chip select) pin - it must be on an unique (separated) pin. All (three) others can be shared with other SD cards (which also must be selected with a unique pin). This is how you connect multiple (even different) devices on a single SPI peripheral.

Anonymous said...

This could be help full to me as i am doing a project which uses the SD card.Thank you very much for your support for guiding us.

Eugen said...

first: greate Job!

i use your code, and it works!
but in 80% "SD card not detected.."
and in if the controller detect a card, its a wrong one "FAT32 not found!" :(
but sometimes everything is working and i can see the file list and the Card Capacity

im using the ATmega32 like you, the only change, i put a level shifter MAX3378 from 5V to 3,3V

i cant understand why the controller so often didn't detect the Card. did you had the same problem? how to solve it.

thx Eugen

Eugen said...

OK! i fix it!
my powersupply did the mistake!
i change to another project with an other powersupply and because i'm so lazzy i just try the other, and it works! 100%

very good programm!
1000 times thank you from Germany!

Rajan Verma said...

Is it feasible to interface sd card with fat-32 protocols with micro sd card

Anonymous said...

Dear Sir, Please give more insight into how to access the files in a memory card using a microcontroller and GLCD without using a Personal computer. e.g. If we interface a touchscreen to uC,in which format the data collected from touchscreen will be stored in memory card? If i want to display images from memory card how can i display them? Any suggestions on this project?Also share some useful links . Please reply as early as possible.Thanks in advance!!

Asif said...

Hello Dear,
Hope so you are doing best of your health and job.
I am facing a little problem with FAT32 library.
When I use 1GB micro SD, files getting corrupt, e.g random folder of strange name appears when SD memory size exceeds by 300MB.
Same problem occurs when I used 4GB sd CARD. after memory 1GB, files getting corrupted...

Can U please help me out is this FAT32 issue OR some firmware modifications required..
Its urgent.. You help in this regards is highly appreciable..

Thanking you in anticipation..

Warm Regards

Amar Gupta said...

thnks a lot for source code atmega 32,
but unable to use it with atmega 8 if u hab collective source like v2.2 , 2.3 , v2.4. plzz tell me or mail me at amargupta196@gmail.com.

thnks a lot..

Avinash said...

I implemented it on AtMega32, 2GB Transcend card. It says Unknown card ditected and FAT32 disabled.
By which I am not able to create files. I was able to write data in raw format but not able read it.
Kindly help me out with this problem.

Anonymous said...

dear sir, unfortunately, we can't get through with your fat files on our sd card. pls help.


shailesh prajapati said...

great job thank for post this from shailesh prajapati,ntpc

Biswaranjan Bhola said...


can you tell me what is the code for initialise the sd card and write a structure value in it and read the structure value

Anonymous said...

How to learn write in C++ like you (uart function)?


ravi kumar said...


I appreciate your work because it is very useful to all embedded software developer. i want to write and read a single character in paritcular location. how do the process.
please reply to my mail id(ravims3679@gmail.com).

ravi kumar said...


I want to write single data on single write in single location of sd card

ravi kumar said...

what is procedure to write and read single location in sd card
please help

Debanjan Sannigrahi said...

Dharmani Sir,

Thank you for creating such a wonderful blogging environment for learning & enhancing our skills in the field of Electronics.

I am fresher to Microcontrollers.

I am using yours concept to be implemented in my project. So I completed the whole circuit as u had given & then burned your code into Atmega32 uC.

Now whenever I am switching-ON the circuit the control goes to infinite loop stating "Card Initialization failed..". How to troubleshoot it ??? Kindly guide me in details...

P.S.: Can u plz give me ur mail id where i can communicate with u, for my further queries ??

My mail id is: debanjan.etengg@gmail.com

sara khodary said...

hi,well done.
how could you use SD card in proteus?
thank you very much.

sara khodary said...

hi,well done.
how could you use SD card on proteus?
thank you very much.

Mohd Haris Siddiqui said...

Hello Sir
am from AMU ,we guys are doing the same project to log temperature data in micro sd card.

i have bought sd card breakout board to supply 3.3 v to card from http://www.onlinetps.com/shop/index.php?main_page=product_info&cPath=75_20&products_id=618

i hv succesfully burned the code but in hyperterminal , am getting an error , it says "no card detected"

am using 2 gb microsd card that we normally use in our cell nowadays.
could u plz help us out. wat are the possible sources of error.
thanks in advance :)

Nihal said...

this is a good site....i would like to share one more site here www.zembedded.com ....i found this equally useful.....Thanks guys

Rudy Hermawan said...

God job Man :D awesome

big Thank's

Sune Brian said...


Good job! But i am not able to read file, could you help me?
> 0: Erase Blocks
> 1: Write single Block 2: Read single Block
> 5: Get file list 6: Read File
> 7: Write File 8: Delete File
> 9: Read SD Memory Capacity a: Show Date & Time
> b: Update Date c: Update Time

> Select Option (0-9/a/b/c):
Send:(03:32:23) 5

1 BMP FILE 86,454 Bytes

I am not able to type in the file name, cause i am not sure how can i find the real file name. Thanks

npeducations said...

very clean and neat explanation

frm: http://www.npeducations.com

Anonymous said...

I am using arduino uno(which has the atmega328p) processor on it.
I tried to change the registers especially in usart and I also changed the port alloction for spi to make this code compatible for atmega328p.but when I run the serial monitor I get the message:"SD card not detected". could you help me with that.
FYI: I use a 8GB SD card.
thanks a lot

hau drauf said...


everything works fine but how to display free memory and total memory in version 2.4.1?

hau drauf said...

oh sry, ive used a wrong main file
from 10 May 2011. problem solved.
big thx for share.

Praveen Kumar said...

sir, i hvae designed the same circuit but i am not able to get anything in the terminal...please help

Lacho Tomov said...

Great project, however the schematics are wrong - CS pin of the sd card is said to be connected to PB1. But in the latest code it's connected to PB4 (SS).

CC Dharmani said...

Hi Lacho,

thanks for pointing that out. Though I've made both the options (PB1 or PB4) available in the sd_routines.h file, the latest code uses PB4 but the schematic shows PB1. I'll update the schematic. Thank you!


Can i use this library for Atmega8?
will i get the memory problem with atmega8 for this library?

Darpan said...

Sir, can you provide me the circuit for connecting sd card to hyperterminal using max232?

miti said...

Great job!
Few small changes and it works great on MEGA164P. Atmel Studio 6.1.

Thank you!

ChristopheS said...

I tested your code and it works fine.
I still have a little problem. It works with a Kingston 4GB SDHC card, but not with my card industrical Swissbit SD 2GB.


I would like to make it work with Swissbit because it works between -40 ° C and +85 ° C.
Have you an idea of the problem?

thank you

CC Dharmani said...

Hi Christophe,

give it a try with reduced SPI speed.

Anonymous said...


Is it possible to use the code without any of the UART routines? I want to interface microSD card with ATmega324.


Feryan R said...

This project is absolutely great sir.
thanks a lot.

I have created an data logger with ATMEGA16 runing 8MHz with Internal Osc.
I try to record date and time first.
I have tried to record it every second, for about 8 Hours. in "ddmmyyyy.TXT" format.

But there is an error. the file is "corrupt", then I run "Check Disk".

the file can opened in text editor, but some date/time was not recorded.

So, can you give suggestion for me sir?

Thanks, :)

Mayur Avhad said...
This comment has been removed by the author.
Mayur Avhad said...

Hello Sir,
Great Work!!!
Thanks a lot!!
This helped a lot in understanding the SPI Protocol,SD card and FAT32 functions.

I am currently working on SDHC card implementation for ATmega16 development board. The clock frequency is 16MHz. Also i am using a SDHC Card of 4GB size by Lexar(my digital camera card).

I have referred your code and tried to implement or my specification but it is not working properly. I am getting all the menu options but when i try to read/write, its not working properly. I cant able to read/write a text file...even read/write a single block sometime not working. also the file list and memory status not showing proper details every time.

Please suggest me the required changes to do in your codes according to my specification.

My email id- mayur.arktechnosolutions@gmail.com

Anonymous said...

i want read file .txt in while(1) but at the second attempt read i get error File does not exist! and the program ends... How i fix it?
my email- j.blonski1991@gmail.com

ChristopheS said...

Hi CC Dharmani,

I bought lots of card with different characteristics: class, capacity, temperature ... I did tested and I noticed a difference between those works and one that does not work:
- One that works are MLC
- That does not work are SLC

How to modify the program to run the SLC?


Anonymous said...


How can i write a table[4] = "1234" to SD Card?

Maha said...

Am quite new to this field. Can you please help me to calculate delay timing with respect to the clock frequency of the mc.

Sidra Khan said...

Hello CC Dharmani,
Thanks for Great Work,
I am using AVR Micro controller running at 1MHz interfacing Kingston SDHC 16GB card. the code resets after printing "High Capacity Card Detected!"
on analysis problem seems in SD_readSingleBlock() at following lines

for(i=0; i<512; i++) //read 512 bytes
buffer[i] = SPI_receive();
Please suggest what might be going wrong.
Thanks once again for the work.

jed said...

This should be ok to implement on a ATxmega with a bit of tweaking hey?

Will I be able to use the USB functionality on my xmega to communicate with the SD card via PC?

my blogs said...

Hi ,

In sd routines.c .... when we send the cmd along with arguments at this line

SD_sendCommand(SD_SEND_OP_COND,0x40000000); //ACMD41

In the command function we rotate the long arg before sending on spi

SPI_transmit(cmd | 0x40); //send command, first two bits always '01'

when we rotate we get some huge values ...WHAT ARE THESE VALUES REFERRING TO ?????( CAN anyone PLEASE EXPLAIN )

Anonymous said...


i'am using a controller with big endian format so i need to convert FAT32.c code to that format,I have converted the code and readfile and findfile are working fine,but i have problem in writefile,So please mail me the FAT32.C code in big endian format,my emailid is ma1833271@gmail.com thanks in advance

Jayachandra Reddy said...

i am doing project "attendance data logger with atmega 2560", for this my application is using 4x4 matrix keypad, 16x2 lcd, sd card and rtc,
first we will create all the students numbers as a folders in sd card, while student entering in to class they will enter their number on keypad that time the "in time&date" will save on their particular folder in sd card, while they exiting from class they will enter their number on keypad again this time"out time" will save on their folder in sd card,
how to do this please give me a suggestions


aadil said...

i was traied the code but it shows sd card detected but not fat32.
it shows fat21 is disabled or fat32 is not found

Anonymous said...

HI MR.Dharmanitech,

i use your code, and it works!
but in 80% "SD card not detected.."
and in if the controller detect a card, its a wrong one "FAT32 not found!"(or)file system is disabled
i am using atmega32.

sampdrrr said...

Please i want fat32 file system sd card tutorial for mikro c dspic

sampdrrr said...

Please i want fat32 file system sd card tutorial for mikro c dspic

Anonymous said...


I tested it with 8 GB SDHC card. It works good. Thank you for your amazing job.

Best regards,
Maciej from Poland

Anonymous said...

Dear Developer,
- A bug which was causing the program flow to go into infinite loop if the character number 512 in a sector was a CR (Carriage Return, '\r'), in the writeFile function. Thanks to David & Piotr M. who pointed it out in the comments.

I am using v2.4.1 but this bug still exists. I'd like to create a file, write some text in it and close with '~'. If i am right your text above is referring to this bug. [lines: 479-500. in the following code: http://pastebin.com/qD5SQysh] Could you please tell me how I could fix this code?

Sumir Kumar Jha said...

Thanks a Lot !!

It work for me, but after some head scratching and wear & tear through your code ....

I ported your AVR code for my MSP430G2553, but I found a problem with your code though.

Problem :
Product Manual SD Card v1.9 from Sandisk say that, SD Card shout remain Asserted though out the (Command + Data Packet + Response). But the Problem I with code is that When you call the function "SD_sendCommand" Its De-assert the CS line right after Successfully Command (R1 == 0), but i create a problem like for Data Packet , because the Assertion should be through a Command Sequence.

I hope, i conveyed the the problem problem, but Please let me know if i misunderstood.


xolbrin said...

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Arduino Price in India said...

it is really a good piece of writing i am doing micro-controller programming for last 3 years but never found such kind of post

Praveen said...

Great post. its very help full for my project work. thank you very much

Piyush Menghani said...

Hey...Isn't is possible to avoid using those level shifting resistors just by using 3.3V all over the circuit? i mean atleast for the circuit without RTC, the atmega and the SD card can both be run at 3.3V?

Anonymous said...

does not work with Elite Pro card 256mb
who can help me ?

Mukudzei Makepeace Mangena said...

I am designing a Digital Audio Player using Atmega32.I am using a microSD card to store (.wav) files.The filesystem being used by the card is FAT32.So far I have successfully initialized the SD card and was able to read the Master Boot Record(MBR) using the code provided on this blog.Now I am stuck on how to read and play files from SD card.Is Anyone who can assist me on how I can translate this code in order to be able at least to read .WAV files.

Anonymous said...


I'm using 2GB SDcard which is being detected but unable to detect 8GB sdcard

Fahad Albasheer said...

can I use LCD to display .txt from SD card?

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