29 Jan
2009
29 Jan
'09
11:52 a.m.
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.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin