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UV EPROM “Over-programming"

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@rt:
Hi Guys :)
While I’m not exactly new to the hobby, I sometimes think “beginner questions” are best asked in here.

There are several references to Over-Programming in the old UV erasable EPROM datasheets,
and other references can be Googled without really explaining what EPROM over-programming really means.

I realise the fast programming algorithms (Presto, Rapid) deliver a shorter pulse and then verify, then pulse again if necessary,
as this reduces the programming time overall, but is there any other negative effect of over-programming?
Cheers :)

MK14:
http://eeshop.unl.edu/pdf/27128.pdf

My interpretation is that the over-programming is a VITAL part of the fast programming algorithm. That must be done to ensure reliable programming of the EPROM.

If you fail to do the over-programming, it may be unreliably programmed.

capt bullshot:
Yes, thats the point.
The repeat until "0" is read pulses bring the necessary charge to the isolated gate. The amount of charge is just enough to cause the memory cell to read the "0". For reliability sake, you need some excess charge on the floating gate, thats what the "overprogramming" does.

bktemp:
From this application note:
http://www.atmel.com/Images/DOC0578.PDF

--- Quote ---memory locations that have been previously programmed can be partially
erased by programming subsequent locations (due to the
elevated voltage on the same row or column in the memory
array)

--- End quote ---
So applying excessive programming pulses may degrade already programmed memory locations. That's why most algorithms program just enough and add a bit more but not too much to avoid changing other memory locations.

MK14:

--- Quote from: bktemp on March 30, 2017, 10:13:24 am ---From this application note:
http://www.atmel.com/Images/DOC0578.PDF

--- Quote ---memory locations that have been previously programmed can be partially
erased by programming subsequent locations (due to the
elevated voltage on the same row or column in the memory
array)

--- End quote ---
So applying excessive programming pulses may degrade already programmed memory locations. That's why most algorithms program just enough and add a bit more but not too much to avoid changing other memory locations.

--- End quote ---

My understanding is that it is the other way round.

If you missed the over-programming, so that it was only just at the logic level '0'. Then programming more locations could make it incorrectly read '1', i.e. be slightly erased.

So MORE, not less programming is required. As implemented by the over-programming part of the algorithm.

tl;dr
It is the "Marginally programmed" bits that they are worried about. Over-programming (and extra verification, extended voltage tests) are trying to reduce or eliminate marginally programmed bits which can be unreliable and not last the 10+ years life time.

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