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Erasing UV EPROMs

S

Shadow Lord

Veteran Member
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Jun 16, 2010
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Location
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Hello All,

By definition can UV EPROMs (i.e. those with a window) only be erased by UV light? I have a cheapo G540 USB programmer and it has an "erase" function which I believe seems to run on an EPROM and completes OK. But reading the chip shows the old content. I have a UV eraser that is not easily accessible at the moment and was trying to get around having to dig it out. Assuming UV light is it, are the old stories about sunlight true? Can I just leave the chip out for a few hours in CA sun and have it be erased? Just wondering...
 
Your programmer wont erase EPROMS (EEPROMS is a different story). In my experience leaving the eprom outside for one week will erase the data fully, I live in a sunny location.
 
From an ST M27C256B datasheet, as one example:

ERASURE OPERATION (applies for UV EPROM)

The erasure characteristics of the M27C256B is such that erasure
begins when the cells are exposed to light with wavelengths shorter
than approximately 4000 Å. It should be noted that sunlight and some
type of fluorescent lamps have wavelengths in the 3000-4000 Å range.
Research shows that constant exposure to room level fluorescent
lighting could erase a typical M27C256B in about 3 years, while it
would take approximately 1 week to cause erasure when exposed to
direct sunlight. If the M27C256B is to be exposed to these types of
lighting conditions for extended periods of time, it is suggested that
opaque labels be put over the M27C256B window to prevent unintentional
erasure. The recommended erasure procedure for the M27C256B is
exposure to short wave ultraviolet light which has wavelength 2537Å.
The integrated dose (i.e. UV intensity x exposure time) for erasure
should be a minimum of 15 W-sec/cm2. The erasure time with this dosage
is approximately 15 to 20 minutes using an ultraviolet lamp with 12000
µW/cm2 power rating. The M27C256B should be placed within 2.5 cm (1
inch) of the lamp tubes during the erasure. Some lamps have a filter
on their tubes which should be removed before erasure.
Click to expand...
 
I think the "erase" function on your programmer is intended for EEPROMs, not UVEPROMs. The latter are erased with UVC wavelengths (approximately 280-100 nm). The atmosphere filters out most of the shorter wavelength sunlight, so you're probably talking days, not hours. That window on the EPROM is made of quartz (fused silica) because it can pass shorter UV wavelengths.

Most EPROM erasers typically use "germicidal" lamps of fairly low power (e.g. 6-9 watts), which should be inexpensive to obtain, unless the Covid-19 folks have snatched them up. My first EPROM eraser was made of a coffee can and a clothes dryer UV lamp. It worked fine.

I note from the above post that the range is given as 400-300 nm, same ballpark.
 
Yeah - one week is not realistic. Time to go digging in the boxes in the garage to get the UV eraser out. Thanks for all the info guys especially the datasheet info.
 
I think I'll test this myself out of curiosity, since there's not much else to do while many of my china packages for projects appear to have been sitting in customs (or whereever) for a month. That said, I do have an eprom eraser already so I wouldn't ever do this in real life.

BTW, this post (convert to english) is interesting on the topic.

https://www.elektroda.pl/rtvforum/topic3236341.html
 
Chuck(G) said:
Just don't overdo it. I've read reports where a UVEPROM was left in the eraser for far too long and would not take programming.
Click to expand...

This is true...

As someone who's erased 1000's of eproms,
I can vouch for the fact "over-erasure" can cause damage.

15-20 minutes in a reliable UV eraser is all you need.
30 minutes max.

If your eproms are not blank after that, they are likely bad.

Steph
 
A good 10-15 minutes is all you need if the lamp is working OK.

I have cards without the sticker over the glass on ROMs that still function after 20+ years.
 
maxtherabbit said:
About 15 minutes seems to reliably blank most things
Click to expand...

Well I can confirm this worked just fine for my EPROM (AM27C256). After the toothbrush treatment I read the rom and all blank. I then tried programming it. Strange thing is I still had two issues:

1. I had to try programming multiple times and then it finally worked.
2. The default seq. in the G540 programmer is to blank->program->verify when I select the above chip. However, it consistently fails on the blank function. What is the blank function supposed to do?

TIA!
 
Seems like you need to adjust the chip type in your programmer software. It should not be trying to blank an EPROM.
 
In the software for the device programmers I use, the Blank function checks whether or not the device is blank before attempting to program it. It would do that by reading the entire device and checking each location for the unprogrammed value. Normally you would not want to attempt to program a device which is not currently blank, and the user would be warned before proceeding.
 
If it's doing a blank check that would be correct, but if it's actually trying to perform an erase ala an EEPROM that would be wrong
 
When I select an EPROM device the default sequence in the software for my programmer is:
Continuity
ID Check
Blank Check
Program
Verify Twice

When I select a FLASH device the default sequence in the software for my programmer is:
Continuity
ID Check
Erase
Program
Verify Twice


Blank Check and Erase are different operations and only one of the two is automatically selected depending on the device type. (Internally there would also be a blank check as part of the erase algorithm to verify that the erase operation was successful).
 
Right, but if you go back and read SLs post he said he manually did a blank check which passed, then the "blank" stage of his programming operation failed. Which seems to me to indicate that it's trying to perform an erase
 
He also said that he tried to program it multiple times before it finally succeeded, but didn't say that he also erased it (with the UV lamp) multiple times. In that case the blank check would pass the first time he tried to program it, and then fail every time after that after it was partially programmed the first time around. But I'm just guessing the most likely sequence of events that makes sense to me.
 
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