29 Jan
2009
29 Jan
'09
1:49 p.m.
Tony Duell wrote:
From the article:
"The contents of the EPROM are continuously read, until all cells read FFh.
[...] Once all cells read FFh, the lamp is left on for about one minute. This
is done to make sure all cells are properly cleared, including those which are
at an undefined state between erased and still programmed."
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
I've never seen a commerical one (but then
I've never seriously looked),
ut I am pretty sure there was a design for ome in one of the magazines
over here <mumble> years ago. Probably Elektor. Given the time, it
probaly only worked with 2764/27128/27256 devices which have essentially
the same pinout, so telling it what sort of device it was erasing is not
a problem.
Rietjens, A.: Intelligent EPROM Eraser. Elektor Electronics, June 1994, p.44-46.
It handles the more common 28-pin EPROMs -- 2764, *128, *256, *512. Can't say
I'd actually bother building and using one, though. 15 minutes is usually more
than enough for most EPROMs and MCUs.
ISTR someone asked why higher-capacity chips take longer to erase. Newer chips
use smaller transistors -- the smaller the transistors, the smaller the
"floating gate" is, and the less SiO2 there is to be hit by the UV. Less area
= less energy absorbed = less charge leakage = longer erase time.
From what I
rememebr, the cirucit just read through all the addresses of
the EPROM until all
of them read as FF. And then geve <n> times more
erasure time. In other words what you expect. I think it was built from
TTL (no microcotnroller, no PLDs of any type), so it should still be
possible to make one.