EPROM erase times and lifespan

Roy J. Tellason rtellason at verizon.net
Thu Jan 29 13:52:24 CST 2009

> Keep in mind that although the output is digital, the actually process of
> an EPROM is analog in nature - the output is decided based on the amount of
> charge on the gate.
> This brings a few important points to understand:
> 1) Some EPROMS are "more programmed" than others.
> Early devices with a fixed proramming time per cell normally are saturated,
> and well programmed. Later "intelligent" algorithms would watch the device,
> note how much charge was needed to make a 1->0 transition occur in the
> cell, add a margin and "your done". Much faster - but depending on the
> equipment, sometimes "less programmed".

I wonder if this has any effect on the longevity of what's stored on them?

> 2) The comparitor is voltage dependant on most devices.
> An EPROM bit near the 0/1 threshold may change state with a difference in
> power supply voltage - Intel spec'd a supply of 6V when using their
> "intelligent algorithm" because that would raise the comparitor voltage and
> cause it to require more charge to get a zero bit. This insured that you
> were programmed "well past" the normal boundary at 5V.
> You can sometimes read an EPROM that is suffering from "bit rot" by
> powering it at a lower voltage.

Ah.  Interesting to know,  I'll have to make it a point to remember that.

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be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
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M Dakin

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