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Bunch of (E)EPROMs...

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New Member
well, as some of you will know, I'm trying to build an eprom programmer (27Cxxx). I have a schematic of what I think suits me, and I'm trying to solve some questions/problems with it.

The question now is this:
As I have no experience with EPROMs, do you think is better to work with 29Cxxx or 29Fxxx EEPROM/flash, rather than 27Cxxx??
If I chosed 27Cxxx because they are cheaper chips. 28Cxxx are SO expensive, and I don't know anything about 29xxxx series, appart from that they are electrical erasable and need only 5V.

Maybe any of you can tell me something about them so maybe I can reconsider my way?? Just to make sure.. I really thank any help.


New Member
Well the 27CXX is much more expansive (about 6$ for a unit) because its an obsolete item and no longer manufactured, in order to erase it you have to put it under an UV light for a long time.

The 28CXX is much cheaper (3$ for a unit) and it can be erased completely with 12V or you can just write another data on it without erasing it.
its access speed is much better then the 27cXX.

The 29cXX is no longer EEPROM but a Flash chip.
It has bigger capacity (up to 8MBit).
Basicly no much diffrences exept accessing speeds and the size factor + Erasing it only with 5V.
The price of the flash is pretty much equal to the EEPROMS with the same capacity.

I would suggest you to build a programmer for both 28CXX and the 29CXXX and drop the 27CXX.
building a programmer for those chips is very easy, i would prefer doing it with MCU like to 80c31 i can give you schematics or explanations if you need.


New Member
Well, what I've seen is taht 27Cxxx can be around 2$ for some chips (like 27C256), and 28Cxxx never go below 6 $, and some get up to 8$. Almost the same aplies to 29Cxxx.
About 29Fxxx, these are cheaper..

Anyway I'd thank you if you could send me those schematics
And also, if someone else has some info or experience about this, I'd like to know. thanks.


New Member
27/28/29 EPROMs

You didn't mention whether you already had a UV chip eraser, it's an additional expense needed for using windowed EPROMs. Windowed ceramic EPROMs are much more expensive to manufacture than plastic flash EPROMs. There are lots of ceramic EPROMs on the surplus market, that's why they're so cheap nowadays. That said, there's nothing wrong with putting 27xxx parts to use in hobbyist projects. It's just more convenient to use flash EPROMs, they are easier to update. Windowed EPROMs usually last for a few hundred program/erase cycles, Flash EPROMs are good for at least 10K, while most EEPROMs today are guaranteed for at least 100K cycles.

I like the 29Fxxx parts, they're inexpensive and only require +5V for programming (as opposed to the 28Fxxx family, which needs +12V). The "5V only" requirement simplifies things if you want to do in-circuit reprogramming. In the U.S., Jameco sells 29F010s for less than the cost of many 27xxx parts.


Although the 29Fxxx series originally came from AMD, you may want to use the Atmel datasheet:

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