68705 r3cs

[Tim Willis]

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I think this chip has a bootstrap program in hardware that is initiated =
when the device is powered up and certain voltages are present on =
certain pins.  What the program does is to read in from an external =
eprom and burn the onboard rom/eprom with the equivalent, when finished =
a programmed signal is produced..  Then the eprom is read again and =
compared, is the two agree the verify signal is output.  The data book =
mentions reading code out, but a small segment of code must be =
programmed into the eprom that can be initiated by the user and code =
would be clocked out of the chip.  Once the real code has been burnt =
this facility is no longer available. =20

The only ways to possibly read the code would be to:
1) Try to burn in the extra code into the device to be able to initiate =
the clocking out of the code.  This would be 1 in a million chance that =
the addresses required as still erased.
2) Trial and error with some circuitry to guess each location of the =
eprom and monitor the reading from the eprom until the verify LED comes =
on.  The circuit would have to act as an erased eprom for the first read =
of each address (this would leave the content of the chip intact during =
first read), and for the verify guess each address' data and monitor the =
verify cycle.  This may not even be possible depending on how the verify =
works.=20

This is all from memory about five years back, so apologies if it is =
inaccurate.

Regards Tim WIllis.


If my mail program truncates lines let me know and
I'll fix the problem.

-----Original Message-----
From:	K PILLAY : STUDENT [SMTP:PILLAYK7 at eng.und.ac.za]
Sent:	Wednesday, September 17, 1997 8:27 PM
To:	diy_efi at coulomb.eng.ohio-state.edu
Subject:	68705 r3cs=20


Does anybody know how to read the code off the eprom on this chip ?
i.e. I have the circuit to program the device but how do you read the=20
stored info to modify and re-store.

Thanks
Kevin

# Too much power is just an ILLUSION !!!!! #


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