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Thread: Serial Flash and 4 Kb sector sizes ? confused !!!

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    Administrator T-1000 vikas's Avatar
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    Default Serial Flash and 4 Kb sector sizes ? confused !!!

    I require serial flash for storing some data interfaced to a pic 18 , it will be availible as a pen drive when connected to PC for easy user updation.

    I had bought Microchip flash but it seems it has 4kb sector sizes, FAT 512 does not really map to 4 kb sector sizes. After looking around people recommended AT45DBseries , due to its 256 byte sector size. Wirting a 512 byte sector seems easier on it.

    But looking at other manufacturers , it seems 4 kb is not being majorly used , So i would like to ask how do you handle 4 kb sector sizes in a microcontroller with 2kb RAM ... All ideas are welcome. Also higher capacity serial flash is available in 4kb sector sizes only.

    Or should i update to better microcontroller ? or stick with AT45DB ?
    Vikas Patial

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    I can recommend you a chip that can save you real amount of money. You are confused little about sectors. It is internal to the device. It is an unit in flash memory that can be erased at minimum. So their is a buffer equal to the size of sector in the device it self. So even if you just want to write a single byte, the internal controller reads the sector in which the target byte resides into the this buffer, then modified the target byte, erase the whole sector, write the whole buffer to the sector again. So from the interface side you can write any number of bytes. This is how all pendrives, SD cards works they have huge sectors but fat works with default allocation size of say 4096 bytes.
    If it has 4096 (4K) sector it will work perfect with PC OSs

    I know a 8MBits flash memory sold at retail for Rs 20/- (yes that means you can possibly buy at around Rs. 5 or 10 MAX ).
    The nice thing is that I have also a code to read and write the memory (in AVR CPU) also to play a WAV file from the memory.

    You can easily write a physical layer that write/read 512 byte sectors and use the

    Also did you forget to read this page
    http://ww1.microchip.com/downloads/e...tes/01045b.pdf (Page 11)

    At minimum MDDFS requires 2121 bytes (All extra functions disabled)

    Also as you wish to make this MSD also the USB MSD Framework need more RAM!

    At minimum I was able to run MDDFS on a PIC18F4560 (SD/MMC)

    I have a wave player for that too.

    I better recommend using a SD Card.
    Last edited by avinash_g; 04-08-2011 at 10:23 AM. Reason: a
    Avinash Gupta
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    Sorry,

    But cheaper Chips don't have the sector buffer I mentioned above. Only SD/MMC cards have it. In SD card we can write any amount of bytes. Mostly the cheap small flash are intended to use like ROMs, so before programming they need a ERASE either a sector, block or chip erase instructions.
    Avinash Gupta
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    Quote Originally Posted by avinash_g View Post
    I know a 8MBits flash memory sold at retail for Rs 20/-
    Hey can you share the part number please.
    Nikhil Chandra | Bangalore

    Imagination is more important than knowledge.

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    Administrator T-1000 vikas's Avatar
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    I exactly know how to handle sectors ... I already did a USB Mass storage device with SPI And SD Cards with pic2550 ... But client wants smaller size with some other weird requirements.

    When moving to 4kb sector sizes the internal ram should be atleast 4 kb + , means pic 24 or above, i find it a overkill for my application . For now i have bought a few AT45DB to get things rolling.

    BTW which chip are you reffering to in 8Mbit , which is Rs 20 ( locally available ) . I will keep this thread posted with the updates ...
    Vikas Patial

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    If you need it just to to any electronic store even the smallest one. Ask him to give the DVD EEPROM IC (Yes they know it by this name). The actual Part number is AMIC A25L080.
    The datasheet is
    http://www.amictechnology.com/pdf/A25L080.pdf

    The reason for cheap price is very mass production of DVD players.

    Anothor compatible one is EON 25T80

    If you can get the eitheir one they are OK. Available in 8 PIN DIP pack. SMTs are not so easily available.
    Avinash Gupta
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    Next time on LRM visit will be sure to ask for it.
    Vikas Patial

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