EPROM Erasing time? 15mins or 55mins is bad?

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Billy Mayo

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When Erasing EPROMS, is erasing the EPROM bad when you use the UV light longer than 30mins?

What do you use to cover up the EPROM so light doesn't get into it? so it doesn't erase it or mess it up?

I have been programming EPROMS chips and between a week or a month the EPROM chips will creates distorted waveforms or digital waveshapes signals or errors , what is the cause of this?

Is it because my UV Erasing Time is set to long?

The datasheets says between 10 to 15 mins when erasing using a 15000 UV lamp light but the UV lamp light I'm using is only 8000 UV lamp to do the erasing

Setting the Erase time to 55 mins will destroy the cells or something in the EPROM chip?
 
Billy Mayo said:
When Erasing EPROMS, is erasing the EPROM bad when you use the UV light longer than 30mins?
Click to expand...

Please show a photo of your eraser. Normally they erase fully in less than 2 minutes but run for maybe 4 or 5 minutes. You can test by programming a chip, then erasing for a minute at a time to see how many minutes before it is fully erased. I did that on mine and 1 or 2 minutes was plenty to erase it, but I run it for about double that.

Billy Mayo said:
...
What do you use to cover up the EPROM so light doesn't get into it? so it doesn't erase it or mess it up?
Click to expand...

Properly you should use a large foil sticker for a permanent cover. For temp cover it doesn't matter, interior room lighting does not emit enough UV to ever erase it. Personally I use a large blob of blu-tack over the window, I'm happy with that for days of use during testing even in sunlight comes in the room.

Billy Mayo said:
...
I have been programming EPROMS chips and between a week or a month the EPROM chips will creates distorted waveforms or digital waveshapes signals or errors , what is the cause of this?
Click to expand...

Unknown! Probably a code error.

Billy Mayo said:
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Is it because my UV Erasing Time is set to long?
Click to expand...

No. What you need is to read the EEPROM, after you program it. I don't know your programmer type but you really need that feature. Provided your programmer can program AND read/verify the chip, all is good as it proves the chip actually contains what you put in it.

If you think the contents of the chip are "going bad" over time you just read it again with your programmer and find out.
 
hi,
At 8000UV a 30 minute UV erasure time should be OK.

Before erasing , always clean the EEPROM window, especially if they have been covered with a 'sticky' label. I find that a rag damped with Meths' works OK.

After Erasing, check that all locations a 0xFF, all '1's.

After programming, Verify the EEPROM contents.

You can buy silvered paper with an adhesive face for EEPROM's.
I used either a small white self adhesive label that I could write on the details of the EEPROM.
A quick option is a black felt tip marker used to black out the window, Meths also removes this ink.

The usual causes of data failure, assuming the EEPROM itself is not faulty, is incorrect programming, due to either the Vpp being incorrect or the program time being too short or exposure to light, especially sunlight if the window is not covered.

E
 
Billy Mayo said:
Thanks for the info.

Yes, what can cause this or what do you think causes EPROM chips to go back over time?
Click to expand...

hi,
As I said.
The usual causes of data failure, assuming the EEPROM itself is not faulty, is incorrect programming, due to either the Vpp being incorrect or the program time being too short or exposure to light, especially sunlight if the window is not covered.

Google for EEPROM principle of operation

https://www.howstuffworks.com/rom4.htm
 
Does it ruin the CELLS inside the EPROM chip if you Erase it longer than 30mins? like 55 mins? does it damage the CELLS inside?

The Cells are like capacitors right?
 
Billy Mayo said:
Does it ruin the CELLS inside the EPROM chip if you Erase it longer than 30mins? like 55 mins? does it damage the CELLS inside?

The Cells are like capacitors right?
Click to expand...

hi,
Look at this link.
https://www.ehow.com/how_7299104_erase-eprom.html

Using Google search could answer most of your questions.

The previous link I posted explained how EEPROM's work.

Do you fully read the posts and links that we post in answer to your questions.?

E
 
on each floating-gate memory cell. If the gate is charged, it will have value of "0". If the gate is not charged, it will have a value of "1". When an EPROM chip is erased, all of the gates are uncharged, so the value will return to "1".
Click to expand...

Do not leave the EPROM chips in the eraser for too long. Overexposure to ultraviolet light can damage the EPROM chip.
Click to expand...

Do you know why Overexposure to UV light damages the Floating Gate Memory Cells inside the EPROM chip?
 
Billy Mayo said:
Do you know why Overexposure to UV light damages the Floating Gate Memory Cells inside the EPROM chip?
Click to expand...

This is an extract from the first link I posted.

An EPROM eraser is not selective, it will erase the entire EPROM. The EPROM must be removed from the device it is in and placed under the UV light of the EPROM eraser for several minutes. An EPROM that is left under too long can become over-erased. In such a case, the EPROM's floating gates are charged to the point that they are unable to hold the electrons at all.

As I suspected you are not fully reading the information we are posting for you.
 
the EPROM's floating gates are charged to the point that they are unable to hold the electrons at all.
Click to expand...

I'm just not sure what these floating ate memory cells are and how they work

So Over Erased Floating Gates will not hold electrons because of why? Are these Floating Gates a FET or transistor or capacitor? or are they Polarized chemicals?

So Over Erasing the Floating Gates does something to the Polarized Chemicals inside the Floating Gates to not hold electrons?
 

Billy...is it really you???

We have being trying to find you for ages. Please come back to the Clinic immediately. Or at least tell us where you are and we will fetch you.

Your Mom is distraught with worry.
 
Programming a UV Eprom charges the floating gate. UV exposure removed the charge from the floating gate. Erased UV proms should read 0xFF's for all locations.

Over exposure to UV light will eventually break down the oxide between the control gate and floating gate but this take a lot of exposure and is what sets the lifetime limit on reprogrammability to several thousand normal erasings. But you can figure several thousand times normal 30 minute exposures as the overall number before reliable programming is effected.

The approximately 1000 hours of UV exposure will degrade the gate oxide layers causing it to be leaky. This may cause the UV prom to lose its programming in a shorter period of time. It still may be months before you see the programming charge leak away to their uncharged (unprogrammed) state.

If you are having problems I would say it is more probable that it is a programmer / software problem or the bulb in your eraser needs to be replaced. UV bulbs don't last very long and their output intensity drops off the more they are used.
 
Last edited:
Thanks for the info.

What can be wrong with the programming or what can I check in the programming?

Theses cells inside the EPROM chip have a control gate and a floating gate, how do they work? And what are these cells called? They aren't photocells
 
Not like a photocell.

1) do you have good UV proms that erase and program properly?

If not then check for all hex FF's after erasing. If getting all FF then it is your programmer. If not then try a known good eraser or buy a replacement bulb for you present eraser.

2) Different UV proms have different programming times and perhaps even different Vpp's. Your programmer should take care of these details unless it doesn't list the particular type of device you have.

Some programmers use 'smart' programming to reduce programming times. They 'kiss' the programming with short programming cycles until it reads back correct programmed value then programmer does an extended burn time based on how many 'kisses' were required, to assure the cell is throughly programmed. Overall this is shorter then a fixed worse case part type programming time. These programers are more prone to have problems as the software is more complex.

UV proms have been replaced with electrically erasable proms and flash memory. UV proms have gone the way of eight track tapes. One time programmable (OTP) parts are UV prom die but no erasing window for UV light.
 
What wee use at work are these

Spectroline PE-140T EPROM Erasing UV lamp

The UV Intensity is 8000 uW power rating

866 Universal Device Programmer BK Precision

Software BK Precision PG4UW V2.89/0S.2012
Universal Control Program for BK Precision Programmers

The EPROM chips we use at work are a AMD AM27C256

1.) To Erase the AMD AM27C256 you need a 12,000 Power Rating UV bulb, but we use a 8,000 Power rating UV bulb
This can be one of the problems we are having at work

2.) Software BK Precision PG4UW V2.89/0S.2012 Universal Control Program for BK Precision Programmers
Has a menus on the toolbar for BLANK, READ, VERIFY, PROGRAM

The READ button Reads what the EPROM chip model is?
The BLANK button checks the address are all Zero 0000s?
The VERIFY button checks the program was loaded?

I don't know how to check the Vpps? what is the Vpps?
I don't know how to check if all the Hex FF's are all erased either? The BLANK button checks all the addresses are all zeros
 
Step back here. Lamp wattage uW and intensity uW/sqcm are two different things. Distance changes intensity, Intensity can be measured usually at a specific wavelength for EEPROM erasing.

Some EE proms when erased are all 1's and some are zeros. The majority are all 1's Check manual.

Vpps. Usually the programming voltage can have zero overshoot. It is very sensitive. I've only used a programming system as part of Single Board Computer. The programming voltage was suggested to be set dead on and only connected via a toggle switch.
 
Well we use a 866 Universal Device Programmer BK Precision, so there is no way to set the Vpps i think?

What does the Vpps mean?

I don't think I can set the Programming voltage on the 866 Universal Device programmer BK precision or can I?
 
You tell the programmer what device you are using, and it sets the programming parameters based on it's internal table.

While UV EPROMs are probably still available, they have't been the technology of choice for years. So I need to ask, how old are the parts you are using and how many program-erase cycles might they have?

Have you considered changing to EEPROM parts? I'm sure that there are drop in replacements available.
 
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