jans@tekcrl.TEK.COM (Jan Steinman) (03/17/88)
<<Kurt>> <Mark> <<...Folks seem to think that seeing the UV light instantly fries your eyeballs. If so, then we'd be blind on the first sunny day. I'll just erase EPROMs this way till I need glasses...>> <...it takes a couple of weeks to clear out an EPROM in sunlight. With my G15t8 bulb it takes 3 minutes, at the surface of the bulb. Thats a factor of 6000 to 1... These suckers are not to be taken lightly.> My understanding is that UV damage to eyes is long term and cumulative. Kurt is right; it won't instantly "fry (his) eyeballs". However, Mark's point is that each erasing exposes you to weeks of sunlight-equivalent UV. Did you know that people (farmers, fishermen, etc.) who spend much of their time in sunlight have a much higher rate of cataract-induced blindness? Let's see if Kurt still erases EPROMS this way after his first cataract operation at age 45! :::::: Software Productivity Technologies --- Smalltalk Project :::::: :::::: Jan Steinman N7JDB Box 500, MS 50-470 (w)503/627-5881 :::::: :::::: jans@tekcrl.TEK.COM Beaverton, OR 97077 (h)503/657-7703 ::::::
agodwin@acorn.co.uk (Adrian Godwin) (02/06/91)
I've seen advertised 'flash eprom erasers' which appear to operate by exposing the EPROM to a flash from a strobe tube, rather than the usual long exposure to a lamp. Do these erasers use anything special, like a flash tube that has lots of UV content ? Or are all Xenon tubes high in UV output ? Could I make one out of a photographic flash, or some other strobe tube ? -adrian
whit@milton.u.washington.edu (John Whitmore) (02/09/91)
In article <5001@acorn.co.uk> agodwin@acorn.co.uk (Adrian Godwin) writes: >I've seen advertised 'flash eprom erasers' which appear to operate by >exposing the EPROM to a flash from a strobe tube, rather than the usual >long exposure to a lamp. >Do these erasers use anything special, like a flash tube that has lots >of UV content ? Or are all Xenon tubes high in UV output ? I think Xenon flash tubes ARE high in UV (and I once had a flash that, when 'popped' into a plaster wall, left a very interesting glowing patch on the wall: the plaster had some phosphorescence). I also think that most photographic flashes will use UV-absorbing glass (and some even use a yellowish filter) to keep the UV from getting out. You may have mixed results erasing an EPROM with a photographic strobe. Still, give it a try; it can't hurt. John Whitmore
wtm@uhura.neoucom.EDU (Bill Mayhew) (02/10/91)
An associate I used to work with told me about an incident at a trade show where a vendor had a prototype board with untaped windows on the firmware EPROMs. A trade paper photographer snapped a picutre, the flash of which trashed the contents of the EPROMs, causing much embarassment for the vendor who was left with a braindead product. ==Bill= -- Bill Mayhew NEOUCOM Computer Services Department Rootstown, OH 44272-9995 USA phone: 216-325-2511 wtm@uhura.neoucom.edu ....!uunet!aablue!neoucom!wtm via internet: (140.220.001.001)
henry@zoo.toronto.edu (Henry Spencer) (02/11/91)
In article <1991Feb10.021307.10532@uhura.neoucom.EDU> wtm@uhura.neoucom.EDU (Bill Mayhew) writes: >... a vendor had a prototype board with untaped windows >on the firmware EPROMs. A trade paper photographer snapped a picutre, >the flash of which trashed the contents of the EPROMs, causing >much embarassment for the vendor ... I'm surprised to hear that it actually erased them; I wouldn't have thought there would be enough accumulated dose from a normal flash. There are a number of cases of such flashes causing *transient* malfunctions, though, and some EPROM manufacturers go so far as to refuse to guarantee normal operation with the windows uncovered -- most any "naked" silicon is photosensitive to some degree. -- "Read the OSI protocol specifications? | Henry Spencer @ U of Toronto Zoology I can't even *lift* them!" | henry@zoo.toronto.edu utzoo!henry
larry@kitty.UUCP (Larry Lippman) (02/13/91)
In article <1991Feb10.021307.10532@uhura.neoucom.EDU> wtm@uhura.neoucom.EDU (Bill Mayhew) writes: >An associate I used to work with told me about an incident at a >trade show where a vendor had a prototype board with untaped windows >on the firmware EPROMs. A trade paper photographer snapped a picture, >the flash of which trashed the contents of the EPROMs, causing >much embarassment for the vendor who was left with a braindead product. With the "proper" electronic flash and the "right" circumstances, the above scenario is quite possible. EPROM's begin to erase with exposure to ultraviolet energy shorter than 400 nm in wavelength. In general, as the energy becomes shorter in wavelength, it's erasing ability increases. Most EPROM erasers use a mercury lamp having a quartz envelope, with the predominant wavelength being being the mercury line at 253 nm. A typical EPROM, such as a 27256, is rated to fully erase with an integrated energy exposure of 15 watt-seconds/cm^2 to the quartz window at a wavelength of 253 nm. A xenon flash lamp, as found in an photographic flash, has enough ultraviolet energy below say, 350 nm to effectively erase an EPROM - given sufficient exposure. However, to be effective for this purpose, the flash lamp must be made of quartz, and there must be no outer plastic filter. Almost all non-professional photographic flash units use a flash lamp made with borosilicate glass (e.g., Pyrex), which significantly absorbs the ultraviolet energy below 350 nm. In addition, such flash units invariably have protective plastic filters, which further absorb any ultraviolet radiation. The combination of borosilicate glass and the plastic filter result in almost no energy capable of erasing an EPROM. Many professional photographic flash units use a flash lamp made of quartz - a necessity for higher watt-second ratings and for short recycle times where lamp heat does not have time to dissipate. A further consequence of higher energy found in professional photographic flash units is that most have no outer plastic filter. In addition, the actual circuit design driving a xenon-filled flash lamp affects its spectral distribution. Xenon lamps with little series inductance in the discharge circuit will exhibit *considerable* energy emission at the Xe(II) lines of 260, 247 and 220 nm. Adding enough series inductance attenuates these emission lines so that the spectral distribution below 300 nm approaches that of say, a 7500 deg K black body. In this latter case, there is still *significant* ultraviolet energy between 300 and 400 nm. The point of the above paragraph is that ultraviolet energy emission of a flash lamp can be considerably influenced by the particular circuit design. The result is that many professional photographic flash units *do* have sufficient radiated ultraviolet energy to erase an EPROM - provided that the flash head is held close enough to the EPROM and/or that enough flashes occur. Since professional photographic flash units have energy ratings between 50 and 250 watt-seconds, it does not require much imagination to see how an integrated energy dose in the watt-second/cm^2 range could occur in a small number of close-up shots. To cause failure of say, a microprocessor-based system does not require complete erasure of an EPROM - in a well-designed system which performs a ROM checksum test upon powerup, all it takes is the failure of *one* bit to prevent operation. I have had for a number of years a Norman A200B electronic flash that I have use for serious photography. This is a portable flash with energy settings of 50, 100 and 200 watt-seconds, and a fast recycle time of 3 flashes/second at 50 watt-seconds. It uses an unshielded quartz flash lamp in front of a metal reflector. This flash produces a significant amount of UV energy. This flash unit *will* trash bits in an 8755 (remember those?), as I once learned through accidental discharge of the flash unit while diddling with a damaged camera connector at a test bench. The flash discharged at 200 watt-seconds about one foot away from an 8085-based board containing the uncovered 8755 EPROM-I/O chip. The problem was immediately evident as the microprocessor system crashed, with hitting the reset button having no effect. At first I thought it was electrostatic leakage from the flash, but then the real cause became obvious. Out of 2K bytes on the 8755, only a dozen or so bytes had random bits set to 1 - but those were enough. I was able to duplicate the failure mode using a freshly programmed 8755. Since more contemporary EPROMS still use FAMOS technology, I have no reason to doubt that that the "right" photographic flash unit will still erase bits if held close enough to the EPROM window. I do not dismiss the story of EPROM memory loss from a photographic flash lamp as "electronic urban legend" as stated by another reader. Such memory erasure has a sound theoretical basis that is substantiated by empirical experience. However, such memory erasure can occur only under a certain combination of conditions as outlined above. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry
agodwin@acorn.co.uk (Adrian Godwin) (02/14/91)
In article <1991Feb10.021307.10532@uhura.neoucom.EDU> wtm@uhura.neoucom.EDU (Bill Mayhew) writes: >An associate I used to work with told me about an incident at a >trade show where a vendor had a prototype board with untaped windows >on the firmware EPROMs. A trade paper photographer snapped a picutre, >the flash of which trashed the contents of the EPROMs, causing >much embarassment for the vendor who was left with a braindead product. This is why I wondered whether a photographic tube (rather than a special UV tube) might work. I've heard a number of variations on the story, often indicating that the machine crashed (due to mis-reading data) rather than suffering permanent washout. -adrian -- -------------------------------------------------------------------------- Adrian Godwin (agodwin@acorn.co.uk)