Blankety blank blank.

[Chris Rhodin]

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All this talk of erasing EPROMs reminded me that the requirements for =
erasing are in the databooks.  From the 1993 AMD EPROM Products manual:

"A dosage of 15 W sec/cm^2 is required to completely erase an EPROM.  =
This dosage can be obtained by exposure to an ultraviolet =
lamp--wavelength of 2537 Angstroms--with intensity of 12,000 uW/cm^2 for =
15 to 20 minutes.  The EPROM should be directly under and about one inch =
from the source and all filters should be removed from the UV light =
source prior to erasure."

The manual goes on to warn that any wavelength less than 4000 Angstroms =
will eventually erase the device and appropriate precautions should be =
used (opaque labels).

>From personal experience (the hard way) I've learned not to trust the =
blank test of an EPROM programmer.  An EPROM is erased when the charge =
stored on the floating gate will not read as 0 (assuming an uncharged =
gate will read as 1) at all combinations of power supply voltage and =
temperature that fall in the specified operating range.  An EPROM will =
read blank on a typical programmer long before the floating gates are =
completely discharged.  My eraser will erase an EPROM to the blank state =
in as little as three minutes.  The recommended erase time for my eraser =
is 20 minutes, that means you should take the time to erase to blank and =
multiply it by seven to get the full erase time.

Chris

----------
From: 	Sandy
Sent: 	Friday, August 14, 1998 11:09
To: 	diy_efi at efi332.eng.ohio-state.edu
Subject: 	Re: Blankety blank blank.

I had this same problem with some older 2716's and 2732, they would not
erase. I left them in for hours! I asked this same question, Is it a UVA =
vs
UVB problem? I think that the lowcost dataerase mentioned something =
about
this, but can't exactly remember.  The solution to the problem was to =
get a
bunch of 2817's and shine it on.  Check your programmer for =
compatibility,
mine needed an adapter board.

Sandy

At 09:51 PM 8/12/98 -0600, you wrote:
>Well, since I've read that an ultra violet lamp can erase
>eproms, I tried it.  Set a timer for 3 mins with my lamp on
>the chip,checked it with the burner, not blank.  5 mins, 10
>mins, 20 mins; not blank.  Got to "The heck with it" and
>left it on for an hour (with six chips under it), still not
>blank.  What gives?
>
>Lamp reads "UV-A Ultra Violet" and "BLE-270W". Wrong
>frequency?  Knowing how well my CSH fits, I made sure to
>take the stickers off the little window.  Left one in the
>sunlight for a (long) while, and it was blank when I
>checked. =20
>
>Yes, I know this is crude.  Yes, I know an eraser is the
>proper way.  Yes I'm going to buy one.  In the mean time,
>why won't these chips erase?
>
>Shannen
>=20


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