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Thread: LOCK down the Flash!!!

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  1. #1
    Join Date
    Jan 2002
    SouthEast (EST)

    29 LOCK down the Flash!!!


    Call me paranoid, but some outside source could re-flash my eprom, and prevent my current custom software from operating. I have already taken software countermeasures to prevent any tampering to my system. It's still possible that I may not have enough software control to prevent a possible unautherised tampering of my system Eprom. I concider this an open "hole in security". This being a potential unautherised invasion of my personal property, I have decided to prevent any changes to this firmware at a HARDWARE level. I DO NOT AUTHORISE any changes to any Eprom code on my machine without my prior concent! In other words, I MUST physically allow it. This makes it MY CHOICE. You too can make this hardware choice.

    If you are happy with the current state of your firmware, and choose to NOT accept ANY unauthorised firmware updates, you can physically prevent any new and most likely undesirable code updates by simply CUTTING 1 pin on the firmware chip.

    Now, this may possibly, in the future, make you "not compatible" with some service offering, but you can always solder the pin back to the board, if you decide to authorise the update, and recieve the "flash" update to be compatable with a future service offering.

    The Flash chip on the Dtivo is:

    If you look at chart:

    Page #6
    TABLE 3

    It will become obvious that you can PHYSICALLY choose to allow updates to the chip based on the input of a single pin on the chip.

    If pin #31 (WE#) is connected to the PCB, it allows the eprom to be updated, because the software can decide what state this input is at. HOWEVER, if this pin is simply CUT from the printed circuit board, it is placed in a state called "High Z", or "Floating".
    It is a determination of the chip to decide what an open connection stat of the chip is, and in this case, a clipped pin as a "floating" , or "high z" state. This is the same state on the chart as a high state. In simple terms, carefully snipping this pin at the circuit board and leaving the posablility to re-connect it, WILL WRITE PROTECT YOUR EPROM!!!!!

    If you want to be anal about it, you can tie the pin to +5v with a 10K resistor, and be 100% positive, knowing it can't be re-programmed.

    I personally didn't snip mine, but placed a piece of wire wrap behind the pin and heated it with the iron, and pulled it out to 90 degrees, like pulling a tooth. I now have the pin outward, and ready for soldering to a switch, if in the future I decide to accept any updates.

    Longwinded, but hopefully usefull.

    Last edited by scanman0; 03-30-2002 at 12:27 AM.

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