29 Jan
2009
29 Jan
'09
10:44 a.m.
On Jan 29, 2009, at 1:39 PM, Ethan Dicks wrote:
I myself did some experiments a couple of years ago at
the South Pole
when I didn't have a proper UV-A bulb (I just had a UV inspection
lamp)... I could get the chips to superficially erase, but when I
built a rig out of sockets and a trim pot to turn down Vcc to the
EPROM for testing, I could reliably read the former contents at
voltages below 5V even when the chips appeared empty at exactly 5V.
Yup, because the bit comparator threshold is determined by Vcc.
Lower Vcc, and you lower the comparator's threshold.
In the end, I gave up on trying to use the lamp I had.
Fortunately I
had a couple of 1MBit FLASH chips and was able to muddle through, but
in the future, I'd probably pack some 27F256s or pack a real EPROM
eraser and use ordinary EPROMs.
Speaking of which, I've recently become enamored with Hitachi
58C256. I bought a tube of them cheap a couple of years ago and
haven't really messed with them until recently. They're very nice
chips; I hope to find some more of them at some point.
-Dave
--
Dave McGuire
Port Charlotte, FL