Difference between "Top Boot" and "Bottom Boot" flash memory

Discussion in 'General Electronics Chat' started by tom66, Jul 30, 2010.

  1. tom66

    Thread Starter Senior Member

    May 9, 2009
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    I did a Google search and found very little information about this, so I thought I'd ask.

    Does anyone know the difference between a "Top Boot" flash memory chip and a "Bottom Boot" flash memory chip?

    http://uk.farnell.com/amic/a25l40pt-f/ic-flash-4mb-spi-top-boot/dp/1566002
    http://uk.farnell.com/amic/a25l40pu-f/ic-flash-4mb-spi-bottom-boot/dp/1566004

    These ICs look identical except one is in stock and the other isn't, so I'd like to order the in stock one (bottom boot) but I'm wondering if it will work for what I want to do (just storing general purpose bits n' bytes... voice data to be specific.)
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    If you look closely you will notice that the pinouts are mirror-images of each other. That is so that they can be layed out on opposite sides of the PCB and connected together conveniently.

    hgmjr
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    I looked at the datasheets you have linked to and what I said does not appear to apply to these devices. These are SPI interface devices so I guess the top and bottom strategy does not apply. The top and bottom strategy applies to those flash devices that have a parallel interface.

    hgmjr
     
  4. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Hmm... well that's interesting. On the Farnell page it mentions something about "sector type" being "bottom boot" or "top boot"... could this have something to do with it?
     
  5. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Does anybody know? I need to buy these chips soon, it looks like I'll be buying the "bottom boot" ones but I want to know if there is a major difference!
     
  6. kingdano

    Member

    Apr 14, 2010
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    just a guess...

    it may be that the default pointer in a top boot device points to the top (or highest hex value) of memory, whereas a bottom boot device points to the bottom (lowest hex value 0x00).

    again, just a guess.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    I cannot see any practical difference between the two types. It seems to revolve around the protection of various blocks of memory within the chip. As near as I can tell there are only two relevant values of the Block Protect Bits which either protects everything or protects nothing. You would think that other values besides 000 and 111 would imply other combinations of protected and unprotected.

    It is also disturbing that Note 2: from Table 1 has no reference point in the text or the contents of the table.

    My guess is that for your purposes I would buy the top boot parts and not worry about it.
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    You can protect sectors of the flash, so they become read only. Refer to table 2 in the data-sheet. On how this protection is arranged in different sectors with different size
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    I disagree that the protection defined by various combination of the Boot Protect bits is either obvious or relevant in the case of the OPs application.
     
  10. tom66

    Thread Starter Senior Member

    May 9, 2009
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    I'm not interested in protection. This will probably be an open source project.

    I may end up using an SD card for this application. So much cheaper for the gigabytes. I can get a serial flash device (SD card, SPI) for £3.99 with 2GB-4GB of capacity on eBay.

    At the moment, the plan is to store voice data (i.e. messages to be spoken) and output these to an audio signal. I will also be doing datalogging. A basic filesystem will be used.
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    I understand that you are not interested in protection. Whichever one you can get will be fine, and yes you can use MMC/SD cards for this application as well. The firmware will be a bit more complicated, but certainly worth the effort given the cost per byte metric and the option to use a higher speed interface with the same command structure if required.
     
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