I’ve come into possession of an EPROM and got a programmer for it. Writing data to it was easy. Erasing data is another matter. Note that I said EPROM and not EEPROM. What’s the difference? An The first E in EEPROM means “Electrically.” And Electrically Erasable Read Only Memory can be cleared by using some electric circuit. The EPROM I have must be erased through UV light. There is a window on the ceramic package that exposes the silicon underneath. With enough UV light through this window, this chip should be erased.

There are devices sold to specifically erase such memory. I’m not using those. Instead, I have a number of other UV sources to test with. These are

• The Sun
• A portable UV phone Cleaner
• A Clamshell UV Phone Cleaner
• A Tube Blacklight

I’m using a M27C256 32k EPROM. To know whether my attempt at erasing worked or not I needed to first put something on it. I filled the memory with binary digits counting from 0 to 255, repeating the sequence when I reached the end. The entire 32K was filled with this pattern. To produce a file with the pattern I wrote a few lines of code.

// See https://aka.ms/new-console-template for more information
byte[] buffer = new byte[0x7FFF];
for(int i = 0;i <buffer.Length;i++)
{
    buffer[i] = (byte)i;
}
using (FileStream fs = new FileStream("content.bin", FileMode.Create, FileAccess.Write))
{
    fs.Write(buffer, 0, buffer. Length);
}

Now to get the resultant file copied to the EPROM. The easiest way to do that is with a dedicated EPROM programmer. They are relatively cheap, easy to find, and versatile. I found one on Amazon that worked well for me. Using it was only a matter of selecting what type of EPROM I was using, selecting a file containing the content to be written, and selectin the program button.

Reading from the EPROM is just as simple. After the EPROM is connected to the programmer and the EPROM model is selected in the software, it provides a READ button that copies all the bytes from the memory device and displays them in the hex editor. To determine whether the EPROM had been erased I will use this functionality. Now that I have a way to read and write from the EPROM, let’s test the different means of erasure.

Using the Sun

These results were the most disappointing. After having an EPROM out for most of the day, the ROM was not erased. Speaking to someone else, I was told that it would take several days of exposure to erase the EPROM. I chose not to leave the EPROM out for this long, as I’d risk forgetting it was out there when the weather becomes more wet.

Using a Portable UV Sanitizer

The portable UV Sanitizer that I tried was received as a Christmas gift at the end of 2022. Such devices are widely available now in the wake of COVID. This unit charges with a USB cable and runs off of a battery. When turned on, it stays on until it is either turned off, the battery goes dead, or someone turns it over. This unit will only emit light when the light is facing downward. I speculate this is a safety feature; you won’t want to look directly into the EV light.

My first attempts to erase one of the EPROMs with this sanitizer were not successful. After several sessions, the EPROMs still had their data on them. While I wouldn’t look directly into the UV light I could point my camera at it safely. The picture was informative. The light had a brighter level on the end that was closer to the power source, and was very dim at the end. Before, I was only ensuring the window of the EPROM were under some portion of the lighting tube. Now, I knew to ensure it was close to the brighter end of the UV emitter. Using the new placement, I was able to erase an EPROM in about 60 minutes.

Provided that someone is only erasing a single EPROM and isn’t in a hurry, I think that this could make for an adequate solution for erasing an EPROM. If there’s more than one though his might not work as well, especially when one considers the time needed to recharge the battery after it has been diminished by an erasing session.

Clamshell UV Phone Cleaner

I received this clamshell UV phone cleaner as a gift nearly a decade ago. This specific model isn’t sold any more, but newer variations are available under the description PhoneSoap. These have a few advantages over the portable UV sanitizer. It runs from a 12 volt power source. There’s no waiting for it to recharge before you can use it. It also appears to be a lot brighter. The UV emitter automatically deactivates when the case is being opened, but there is a brief moment where the case is just being opened but the light hasn’t turned off yet in which some of the light spills out of the unit. It is either a lot brighter, or it has more light in the visible spectrum. The unit I use has emitters on both the hinged and the lower area of the case. EPROMs placed in it could be oriented face-up or face-down and still be erased. When this case is closed, the emitter turns on for 300 seconds and then turns off. I’d like for it to be longer for my purposes, but 300 seconds isn’t bad. After I let an EPROM sit for one 5-minute session in the sanitizer, it still has data on it. But after a second 5-minute session it showed as erased. I think this unit is worthy of consideration.

Tube UV Light

I have an old UV tube light that I purchased in my teens. I dug it up and found a power supply for it. The light still works, but after leaving an EPROM in direct contact with it for well over 24 hours I found no change. I speculated that this would be the outcome for a few reasons. Among which is that UV lights of this type are commonly where people can see them. The cleaning UV lights have warnings to keep them away from skin and eyes. From the glimpse that I got of them through the phone’s camera, it looks that they are working in a different wavelength. Not that this is a true measure of the true bandwidth. But there’s not much to be said about the tube light.

The Winner

The clear winner here is the clamshell UV light. It was easy to use and was able to erase the EPROM in ten minutes. The portable UV cleaner comes in second. The other sources didn’t cross the finish line given a generous amount of time to do so. It might be possible to eventually erase an EPROM with them, but I don’t think it is worth the time.

Now that I have a reliable way to erase these EPROMs, I can use these in the MC6800 Computer that I was working on.

Mastodon: @j2inet@masto.ai
Instagram: @j2inet
Facebook: @j2inet
YouTube: @j2inet
Telegram: j2inet
Twitter: @j2inet

Posts may contain products with affiliate links. When you make purchases using these links, we receive a small commission at no extra cost to you. Thank you for your support.