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Serial number rom ic, with spi or i2c interface?

Discussion in 'Electronic Design' started by Adrian Hjelmslund, Jan 25, 2006.

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  1. Hi group.

    I'm searching for a "serial number ic" which is a rom device with a
    pre-programmed unique serial number.

    Till now I've only found the Dallas DS2401/2411
    (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3711) but it's with a 1-wire
    interface and I'm not so eager to use that.

    Can anyone recommend a device that have SPI or I2C interface and with ROM'ed
    serial number?

    Thanks in advance
    Adrian
     
  2. Guest

    If you can't find one... a cheapo 8-pin microcontroller from Microchip,
    Atmel, etc.
     
  3. There are also some eeproms with write-protect block locking facilities.

    Note that most of these type of devices are fairly easily circumventable so should not be relied
    upon for secure applications.
     
  4. Guest

    With a micro you can implement a reasonably secure challenge-response
    system. The weak point then probably becomes the chip's code protection
    mechanism.
     
  5. Agreed.
    This would be more secure than most of the EEprom type devices which use password type access
    control, or write-once/password-write devices that can simply be replaced or emulated.
     
  6. Thanks guys :)
    Anyway, my problem is not security, but a simple matter of lazyness :eek:)
    Most important for me is that it's preprogrammed, so I dont have to do
    anything other than mount the device and read the id number.
     
  7. they ponyprog eeprom writer software has an auto-increment serial
    number function


    martin
     
  8. FAIK Dallas is unique. But what's the problem with that 1-wire interface?
    It's as easy as :) or as difficult as :( SPI or I2C. Only if you have
    absolutely no pin left for it and you need to connect it using an existing
    SPI- or I2C-interface you can put a micromicro in between. So an eight or
    six pins Microchip or AVR. Of course it makes it little easier for the bad
    guys to fiddle with it but you can easily find this out if you need to.

    petrus bitbyter
     
  9. Paul Burke

    Paul Burke Guest

    It's an absolute pig if you have multitasking or interrupts, because
    unlike SPI and I2C, you can't just hold levels in mid- process. So he'll
    have to read it before that bit of the program starts.

    Paul Burke
     
  10. Guest

    I've used the 2401 in a number of projects. What I usually do is to
    read it as part of the startup sequence and store the contents into RAM
    before interrupts are enabled.
     
  11. Guest

    If the serial number is not "special" then maybe you can implement it
    in on-chip EEPROM. When you power the unit up for the first time at the
    factory, you can either have the tester enter a number on the local
    interface, or use an external or internal [pseudo]random source to set
    the serial#.
     
  12. Well.......that statement requires a bit more qualification. There are
    places you can't pause due to timing or power constraints, but you can
    pause between the bit sequences for days if you like.
     
  13. Thanks guys, you've been very helpfull.

    I've been thinking bit more and I think I have to stick to the 1-wire
    solution eventhough I'm not too happy about it.

    Problem is that it is timing dependent and that I don't have other 1-wire
    devices, so it will feel bit messy to implement it just because of a serial
    number, but the alternatives aren't much better I must say.

    I came to the conclusion that Bobs solution about reading during the
    initialisation process, before enabling other interrupts or timer, is the
    solution that suits me best.

    Thanks for advices and inspiration :)
    Adrian
     
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