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'[EE] EPROM or flash for storing code?'
2006\11\27@175740 by John Waters

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Hi All,

I used to use a EPROM for storing code, but I found that some circuits use
flash for storing code instead. What is the difference between these two
ways of code storage? Which is better?

Thanks in advanced!

John

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2006\11\27@182714 by Jinx

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> I used to use a EPROM for storing code, but I found that some
> circuits use flash for storing code instead. What is the difference
> between these two ways of code storage? Which is better?

Hi John, AIUI, the retention times for both are 40+ years. EEPROM
can be written to 10x more than Flash, typically 100k min vs 10k min,
and on a single byte basis, rather than blocks. If this is seldomly-changing
data (eg parameter modification or "learning") then either EEPROM or
Flash will do

Microchip have a number of ANs for EEPROM that are worth
reading. They cover the write mechanism (eg using lower Vcc to
maximise write endurance) to maximising writes in an array

Dig up ANs 536, 537, 562, 601, 602, 1019

TB072, "Flash memory technology : Considerations for design"

http://ww1.microchip.com/downloads/en/AppNotes/91072a.pdf

2006\11\27@193734 by Paul Hutchinson

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> -----Original Message-----
> From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu On Behalf Of John Waters
> Sent: Monday, November 27, 2006 5:58 PM
>
> Hi All,
>
> I used to use a EPROM for storing code, but I found that some circuits use
> flash for storing code instead. What is the difference between these two
> ways of code storage? Which is better?

Flash is electrically erasable, EPROM erases with UV light.
Flash can be easily programmed in circuit.

This article from Michael Barr's Embedded Systems Glossary should help.
http://www.netrino.com/Publications/Glossary/MemoryTypes.html

Paul

PS - Jinx I also read the question as EEPROM at first ;-)

>
> Thanks in advanced!
>
> John
>

2006\11\27@195249 by Jinx

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> PS - Jinx I also read the question as EEPROM at first ;-)

I'm sure John means EEPROM. There probably is some in-
circuit usage of EPROM but EEPROM would be much more
usual these days. Although I think un-windowed OTPs are
EPROM. I guess not having to include the "Electrically" part
would make it cheaper. From what I can gather, the distinction
between NV families is often blurry. There are many technologies
to make NV and one family could simply be a minor variant of
another

2006\11\27@202638 by Ling SM

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>>I used to use a EPROM for storing code, but I found that some circuits use
>>flash for storing code instead. What is the difference between these two
>>ways of code storage? Which is better?
>
>
> Flash is electrically erasable, EPROM erases with UV light.
> Flash can be easily programmed in circuit.
>
> This article from Michael Barr's Embedded Systems Glossary should help.
> http://www.netrino.com/Publications/Glossary/MemoryTypes.html

I have been suspecting that Flash or EEPROM are not as rugged on the
field as EPROM.  Most likely due to surge, EPROM when it fails, it is a
device failure.  UV does not help.  But a good percentage of Flash or
EEPROM can be recovered through reprogramming.  Comments?

Cheers, Ling SM

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