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Execution and Reading from parallel EEPROM

Discussion in 'Embedded' started by Ammulu, Oct 6, 2003.

  1. Ammulu

    Ammulu Guest


    I am working with parallel EEPROM and the application is as follows:

    The code will be executed from parallel EEPROM and i require to read
    total contents of the same parallel EEPROM, Which i am unable to read.

    Is it possible in EEPROM to read the when executing from the

    I am using AT28HC256 EEPROM.

    Pls let me know the information on the above at the earliest.

    Thanks in advance,
    Ammulu, Oct 6, 2003
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  2. Unable why? How exactly did you try to do it? What's preventing you
    from succeeding to do it?
    Depends on what CPU you're using. If it's a von-Neumann architecture,
    it should know how to disentangle code fetches and data memory access
    properly. If you've von-Neumann'ed a Harvard architecture processor
    by means of external chip select logic, you *might* be in trouble.
    Hans-Bernhard Broeker, Oct 6, 2003
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  3. Ammulu

    Yvan BOURNE Guest

    You have to copy your code in RAM (code which read or write in EEPROM) and
    execute it in RAM. After these operations, you can return in your EEPROM

    Yvan BOURNE, Oct 6, 2003
  4. Ammulu

    Henry Guest

    Depends on CPU/controller used. Please specify.
    I think you mean writing AND excecuting code of the EEPROM at the same time.
    This is not possible. The EEPROM is locked until write has taken.
    - Henry

    Ammulu schrieb in Nachricht
    Henry, Oct 6, 2003
  5. Ammulu

    Wade Hassler Guest

    If you can execute code from a 28HC256 EEPROM you *are* reading it.
    Perhaps your processor is configured to treat the device as
    CODE-memory only, using another memory-space (or chip-select) for DATA
    Wade Hassler, Oct 6, 2003
  6. Ammulu

    Ammulu Guest


    I am using Motorola 68332 Microcontroller(basically CPU32 arch).

    I need execution and reading from same EEPROM.

    When I am executing the same code from RAM, i am able to read entire
    EEPROM to calculate the CHECKSUM of the same code.

    I am not able to read the entire EEPROM when executing the code from
    EEPROM, it should be noted that the code being executed is also to be
    read for my purpose.

    pls give more information for the above

    Thanks in advance,
    Ammulu, Oct 7, 2003
  7. Ammulu

    Tauno Voipio Guest

    How does it show that you're not able to read the EEPROM data?

    Are you sure that there are no locations written in the middle of the code?
    The data of the code can be in the same meory block if the code is run from
    RAM, but the data must be located to the RAM separate from the EEPROM when
    running code from the EEPROM - you *cannot* use the same piece of binary
    code. Check your linker map.

    Been there - done that (with a 68332) - it does work properly done.


    Tauno Voipio
    tauno voipio @ iki fi
    Tauno Voipio, Oct 7, 2003
  8. Ammulu

    Wade Hassler Guest

    You say you can boot up but not read the entire EEPROM(?)
    The default size of the boot-ROM chip-select is 2Kbytes; to address a
    28HC256 you must change the size to at least 8Kbytes

    Another possibility: you _may_ have the CPU configured for separate
    data/code spaces: check the reset-time setup (certain data lines are
    pulled down by reset to configure the operation.)

    Also: are the wait-state settings correct? Parallel EEPROMs are slow.

    (This is based on experience with the 68HC16, which has the same
    peripheral interface as the 68332.)

    Good luck. It'll be fun once you get past the bumps
    Wade Hassler
    Wade Hassler, Oct 7, 2003
  9. Ammulu

    Ammulu Guest


    I am writing data to parallel EEPROM through programming tool right now.

    Is it possible to write parallel EEPROM through software ?

    If possible, is it through alogrithm or through proper timing of control signals ?

    I could find alogrithm for chip erase of parallel EEPROM .


    Ammulu, Oct 9, 2003
  10. Ammulu

    Tauno Voipio Guest

    Get the data sheet of the EEPROM chip you're having. It tells how.

    Tauno Voipio
    tauno voipio @ iki fi
    Tauno Voipio, Oct 9, 2003
  11. Ammulu

    Yvan BOURNE Guest

    Yes, you can write to tour EEPROM through your embeded software, but the
    function to do this MUST be executed in RAM.
    There's no algorithm to write in EEPROM (28Cxx I think...), it's like an RAM
    write, but the difererence is a delay after the WR pulse before an athoer
    access to the EEPROM. This delay is the time that the EEPROM spend to write
    the byte inside its memory array (have a look at "DATA polling" and "Toggle
    bit" in the datasheet).
    So, there is no algorithm for these type of memory (except to lock and
    unlock "software data protection").


    Yvan BOURNE, Oct 9, 2003
  12. Not necessarily. It just must be executed _somewhere_ else than the
    EEPROM you're writing to. Could be anything, really. RAM, a
    boot-loader PROM, CPU-internal code memory if your chip has any, or
    just a second EEPROM.

    If the micro in question is a Harvard architecture, wiring a
    von-Neumann RAM section just for this might be a waste of effort, and
    one of the other methods would work better.
    Hans-Bernhard Broeker, Oct 9, 2003
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