Quote:
Originally Posted by Mark1960
I’ve read a few times in different fora that one method of recovering data from an eprom that has started to lose its memory due to old age is to vary the supply voltage. If this is correct then reading the eprom at 3v3 might not mean it would work correctly in its original 5v system.
Also if you read an eprom and find it doesn’t match the required content, how do you know if its because you read it at 3v3 instead of at 5v.
For fault finding its probably better to read devices as close to the correct spec as possible.
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Well some EPROM-Programmers, like Dataman / ELNEC ones (and probably v.expensive Data-I/O etc) do "Voltage-Margining" when verifying a device (after programming etc). using Vcc +/-5% or 10% (sometimes configurable)
And I have sometimes found ones that won't read the same at one of these, compared to nominal Vcc / the opposite Vcc margin voltage.
IIRC, it is reading at the upper-voltage that is most-likely to give problems, due to internal reference-point scaling with Vcc. So setting Vcc at lower limit may give you best chance
But operation below the EPROM's min. Vcc spec. may not work (especially over temperature) and I think CMOS ones don't have a lower Vcc spec. (Unlike 74HC logic)