I
Ian Malcolm
Guest
Lostgallifreyan wrote:
sunlight and IIRC individual memory cells could be affected in a matter
of weeks of direct sunlight. Of course it would take *much* longer for
the whole EPROM to read blank - especially in our climate.
I *may* still have some of my notes from the time, but they are in dead
tree format and aren't practically searchable (not to mention lousy
handwriting). One thing to bear in mind when setting up such an
experiment is that ordinary window glass is a fairly effective UV filter
and also you need a sunlight recorder (the sort that burn trails accross
the daily paper if you want repeatable results. A lot of work for a
hobbyist for not much knowlage. ONE student engineer probably did some
research back in the early 70's and by the end of that decade, it was
commonly accepted that one *did* cover the windows. Whether later
generations of EPROMS are as vunerable to daylight as say a 1702, is
another matter. I suspect that in the interests of long term data
integrity, later chips may be effectively 'hardened'.
A 1702 datasheet gives the requirements for erasure as shortwave UV
(UVC) at 2537 angstroms with an integrated exposure of 6 watts/sec/cm^2.
UV levels at sea level (tropical) peak at about 0.13 milliwatt/cm^2 at
about 5000 angstroms. UVC is effectively totally removed by the ozone
layer. *IF* UVB was as effective as erasing eproms as UVC, then a 1702
would be totally wiped by 13 hours of direct sunlight. The intesity of
UVC at about 2500 angstrom *outside* the earth's atmosphere is of the
close order of 0.01 milliwatt/cm^2, so an EPROM in *ORBIT* protected
against UVB but *NOT* UVC would be totally erased in 600 hours of
sunlight. Add in the variable effects of cloud cover, strength of the
ozone layer, possible inadequate programming of the EPROM in the first
place, and reduced exposure to flip the first bit rather than wipe ther
whole array etc. I see no reason to doubt that the effective life of the
data in an unprotected EPROM exposed to direct sunlight is of the order
of weeks, not years. One thing is for sure, I am not digging out one of
my remaining few 1702s and breadboarding a programmer to do any tests
I do know that there are confirmed reports of ordinary bench or room
lighting upsetting the operation of windowed EEPROMS and for the price
of a roll of foil tape, one has guaranteed 100% effective light barrier.
I've never experimented with the effect, decapped DRAM with a suitable
lens over it was *much* more interesting!
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:
Well I was taught many many moons ago, that an EPROM could get wiped by
sunlight and IIRC individual memory cells could be affected in a matter
of weeks of direct sunlight. Of course it would take *much* longer for
the whole EPROM to read blank - especially in our climate.
I *may* still have some of my notes from the time, but they are in dead
tree format and aren't practically searchable (not to mention lousy
handwriting). One thing to bear in mind when setting up such an
experiment is that ordinary window glass is a fairly effective UV filter
and also you need a sunlight recorder (the sort that burn trails accross
the daily paper if you want repeatable results. A lot of work for a
hobbyist for not much knowlage. ONE student engineer probably did some
research back in the early 70's and by the end of that decade, it was
commonly accepted that one *did* cover the windows. Whether later
generations of EPROMS are as vunerable to daylight as say a 1702, is
another matter. I suspect that in the interests of long term data
integrity, later chips may be effectively 'hardened'.
A 1702 datasheet gives the requirements for erasure as shortwave UV
(UVC) at 2537 angstroms with an integrated exposure of 6 watts/sec/cm^2.
UV levels at sea level (tropical) peak at about 0.13 milliwatt/cm^2 at
about 5000 angstroms. UVC is effectively totally removed by the ozone
layer. *IF* UVB was as effective as erasing eproms as UVC, then a 1702
would be totally wiped by 13 hours of direct sunlight. The intesity of
UVC at about 2500 angstrom *outside* the earth's atmosphere is of the
close order of 0.01 milliwatt/cm^2, so an EPROM in *ORBIT* protected
against UVB but *NOT* UVC would be totally erased in 600 hours of
sunlight. Add in the variable effects of cloud cover, strength of the
ozone layer, possible inadequate programming of the EPROM in the first
place, and reduced exposure to flip the first bit rather than wipe ther
whole array etc. I see no reason to doubt that the effective life of the
data in an unprotected EPROM exposed to direct sunlight is of the order
of weeks, not years. One thing is for sure, I am not digging out one of
my remaining few 1702s and breadboarding a programmer to do any tests
I do know that there are confirmed reports of ordinary bench or room
lighting upsetting the operation of windowed EEPROMS and for the price
of a roll of foil tape, one has guaranteed 100% effective light barrier.
I've never experimented with the effect, decapped DRAM with a suitable
lens over it was *much* more interesting!
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL: