Can you name this tune?

[Teller.John at orbital.com]

A very cheesy way to copy protect your product.  They risked problematical reads
of the EPROM by the ECU for very little security as the copy protection scheme
seems trivial to defeat!  So much for that.

It sort of reminds me of the goofy copy protection schemes the software
publishers used back in the 80's for my Commodore-64.  They worked so well at
times, that the computer was unable to run the game because the scheme relied on
quirks that were different on each batch of computers!

--- John T.


>There are usually the equivalent of diodes on inputs that provide esd
>(electrostatic discharge) protection.  These diodes try to prevent the
>input from going above vcc or below ground (by more than the voltage drop
>across a diode).  Above vcc means above pin 28 and below ground means
>below pin 14 because this is where one side of each diode connects to.
>So, you can attempt to power the eprom through the inputs because the
>power will find a path through the diodes. This has a better chance of
>working if the eprom is driven with cmos drivers (like a 68hc11) since the
>outputs tend to go close to vcc when driven high or close to gnd when
>driven low.  An input may even be tied high or low (vpp on the 27256?).
>Don't forget about vpp, ce and oe when considering if there is at least
>one input high and one input low.
>
>The above is not intended to be a definitive answer of why it works, but
>it's my guess.
>
>My eprom programmer uses ttl drivers and vpp is not tied high (it can't be
>tied high if it supports a 27512).  Therefore, I would expect problems
>trying to read an eprom with the vcc and/or gnd pins cut.