EPROM erase times and lifespan

[Philip Pemberton]

Tony Duell wrote:
> th return ot the 'intellegent' EPROM ereaser, my worried is that do we 
> _know_ that the rest of the chip (addresss decoder, sense amplifiers, 
> etc) will work correcting when irradiated with short-wavelength UV? In 
> other words is the readout of the chip even meaningful under such conditions?

I'd go with "maybe, but it isn't guaranteed".

To my knowledge, no EPROM manufacturer (if there are any left, I seem to 
recall STMicroelectronics were one of the last) guarantee that their chips 
will work under UV light -- I suspect the expectation is that you hit them 
with UV light for one reason only -- to erase them. There may be a little bit 
of shielding over the more sensitive circuitry, but I wouldn't bet any money 
on it.

One thing that's sometimes worth a quick demo is the propensity of EPROMs to 
temporarily lose their programming when nailed with high-intensity light from, 
say, a camera flash. That caught me out a few times -- I've got a couple of 
old HTEC "Kitty Card" 8052 microcontroller boards (formerly sold by 
Greenweld). Basically, it's a board with an 8032, an EPROM, a bit of RAM, an 
RS232 line-driver and a few I/Os (notably a HD44780 LCD driver). The original 
code in the EPROMs contained text referring to the old Argos "Premier Points" 
scheme.

Anyway, I finished hooking the board up, and figured it'd be nice to have a 
photo of the whole arrangement. The camera flash fired and the software 
promptly crashed.

A nice explanation as to why semiconductors tend to come in light-proof 
packages, and why you really should put reflective labels on windowed ICs when 
you're done playing with the software...

-- 
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/