Re: Sider/ SASI Info

[mjmahon@aol.com (Michael J. Mahon)]

Bill Garber replied:

>> >The Rom is an 2732 eprom, and
>> >the sticker is totally worn off exposing the window fully and more than
>> >likely has been partially or even completely erased.
>>
>> Don't worry.  Unless it has been left exposed to full sunlight for many
>> hours, it's probably fine.  EPROMS are not like photographic paper!
>>
>> If the EPROM is used indoors, it is not even _necessary_ to cover
>> the window (although it is always _advisable_).  (Unless you keep
>> a frequently-used flourescent light within a foot of the EPROM.  ;-)
>
>Thanks Michael. I thought that was true, but I also heard that
>sometimes those things simply lose their program after many
>years of non-use. I know some of my Atari eproms that were
>close to 10 years old would do that, but I kept files of them
>and could burn new ones when they did. ;-)

Keeping copies is an excellent precaution.  EPROMs do decay
slowly, since their programming is retained by a small amount of
trapped charge associated with each bit.  It is possible to both
"underprogram" and "overprogram" an EPROM.  If one is under-
programmed, its programming will decay faster than the specs
would indicate, and if overprogrammed, it may not be able to be
fully erased.

Generally, professionally burned EPROMs are well programmed
and should outlast their "specified" life, but, manufacturing being
what it is, an occasional batch may be marginally programmed,
which might not cause a problem for years.

Prolonged exposure to UV-containing light will accelerate the
decay of the trapped charges, leading to a (usually partial) loss
of programming.  (Complete erasure actually requires a _lot_ of
short wavelength UV exposure--enough to cause a very serious
"sunburn" for a human.)

The upshot is that even though EPROM programming is generally
fine, and accidental erasure is unlikely, those copies may eventually
be needed...   ;-)

-michael

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