BigEd wrote:
Found it - it wasn't erasure in this case, but photoelectric disturbance...
Here,
here and
here.
Yes, and all three of these posts refer to the same incident (involving the EPROM-based 68HC705 microcontroller).
There was one other EPROM incident, but I'm presently unable to find a post about it. Maybe no such post exists, so...
Back in the early or mid 80s I was troubleshooting my expanded KIM-1; I think it might've been after a certain accident that sent 110VAC into the 5V logic (ouch!!). These and many other details are foggy after all this time. But as a "logic probe" of sorts, I had a couple of 4029 counters whose divided-down output fed into a small loudspeaker. (The human ear is astonishingly sensitive, and I'd successfully used similar tricks in the past.)
I don't recall which KIM-1 signal I was probing, but the speaker was producing a steady, audible tone... Steady, that is, until I happened to move my hand near the KIM, and that's when the pitch (ie, frequency) suddenly skyrocketed.
Through some fluke, what I seemingly had in front of me on my workbench was a
Theremin!
At first I thought the frequency change was due to the capacitance of my hand approaching the circuitry, but that theory was quickly disproven. In fact the change was due to the shadow of my hand falling on the (unprotected) window of a 2716 EPROM. To this day I can't imagine how light got translated into
frequency, but I promise I'm not making this up. And it was a
very, very sick computer, with many damaged chips.
-- Jeff
_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html