Basic questions on EEproms

Discussion in 'General Electronics Chat' started by Autofix, Jan 17, 2007.

  1. Autofix

    Thread Starter New Member

    Jan 17, 2007
    4
    0
    Hi all,

    I am very new to electronics and only have a very basic understanding. I find myself needing to understand a bit more all the time. Hope someone here can give me some advice.

    A bit of background before I ask a few questions, which I hope is ok.
    I work in Automotive Diagnostics. Most of my work involves sorting faults in the sensor and supply circuits external to the control units in cars. More and more I find the need to get involved with the control units themselves. For example, if I want to change a control unit it normally needs to be coded or it might need transponder chip keys matched. swapping eeproms can often sort this. Some of this work I can do with pc based software. Basically all the software is doing is reading the eeproms and extracting some code to convert to decimal. There are also a lot of corrupt eeprom problems which could be sorted by copying from another unit the same and editing to suit.

    For now I would like to hear of good sources where I can read up a bit on eeproms to gain a better understanding. For example, I dont understand checksums.

    Thanks

    Autofix
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,789
    EEPROM - Electrically Eraseable Programable Read Only Memory. There are two flavors depending on how the data goes in and out. A parallel interface will read and write information a byte(8 bits) at a time. In general the read time is very much faster than the read time by several orders of magnitude. One example might be a read access time of 200 nsec. and a write time of 10 milliseconds.

    Another type is a serial interface where the data gose in and out of the chip a bit at a time. The read time depends on the speed of the serial interface. The write time may still be in the range of 10 milliseconds.

    A checksum has nothing to do with eeproms per se. It is a checkword for a dataset which is computed by adding up all the data words. It is used to detect certain types of errors. A more sophisticated error check is the CRC - Cyclic Redundancy Check, or the related ECC - Error Correcting Code.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    A good way to learn more about eeprom devices is to go to the website of a manufacturer of the devices and study one of the many datasheets that they provide.

    As an example you can visit the Atmel website and find datasheets for both the serial and parallel type devices that papabravo mentioned in his reply.

    Here is just one datasheet to give you a for-instance.

    hgmjjr
     
  4. sci-3d

    Well-Known Member

    Aug 22, 2006
    51
    0
    Primary reference is Wiki.
     
  5. Autofix

    Thread Starter New Member

    Jan 17, 2007
    4
    0
    Hi all,

    Thanks for the replies and sorry for being so long in coming back. It can be difficult to find the time to play with these things.

    So far I have bought a hot air station and learned to use it quite well. Lucky I practiced on old boards! By quite well I men I am no longer burning PCB's :) I bought a simple programmer which is called SI Prog and works with PonyProg by Lycos. I have been reading a few forums and this has thrown up a few more questions.
    I tried to read an eeprom which was supposed to be a 93C46 according to the info I have on the control unit I got it from. It is marked 47AX858323 so not sure that is the same. My intention was to modify the dump and write it back so as to make the unit run without an immobiliser signal. I read the dump with the intention of saving it first in case anything went wrong but it did not look right. it was all zero's. I soon discovered that every time I read it I got a different result. By this I mean that the dump was different and the CRC was also different. Is the CRC not the same as checksum and should it not be the same every time? I can post the dumps if anyone wants a look.

    Has anyone any idea what is going on here?

    Thanks

    Alan
     
  6. Dennis Atwood

    New Member

    May 26, 2007
    8
    0
    CRC stands for cyclical redundancy check. it's basically the same thing, yes, it should be the same each time.

    maybe you've got a loose connection between your chip and the reader? you said you're using a hot-air station, are these surface mount chips? how are you connecting them?
     
  7. Autofix

    Thread Starter New Member

    Jan 17, 2007
    4
    0
    Hi Dennis,

    Thanks for the reply.

    Yes, the eeprom is SMD. I had it soldered onto an adapter. There was a bad solder joint under the adapter. Once I found that everything was ok.

    Thanks

    Alan
     
  8. Autofix

    Thread Starter New Member

    Jan 17, 2007
    4
    0
    Hi,

    Another question if anyone is up for it.

    I have read a few times about "mask" but have no idea what this refers to. For example I have heard of Mcu zc422428cfn with mask 3d33j.

    Anyone any idea what mask refers to?

    thanks

    Alan
     
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