Why I can`t erase eeprom?

[vedo35]

Hi everybody i had some old cd drivers. On cd driver pcb`s i picked eeprom`s from winbond PLCC32 type W27C512p and 27e257p. I looked to datasheets this eeproms normal eeprom. you can reprogram and erase with universal programmer. i am looking to datas with read. i wanted to erase because i dont need data inside of this eeproms. But always erase error message giving. I checked plcc32 socket and pin direction. Everything ok. Somebody know about this or somebody had same problem(s) before?

By the way i am using galep-4 universal programmer.

I was thinking maybe software protection or write / erase protection. But before i found a lot of mcu`s and flash with program protect i was erasing without problem.
Waiting your ideas or advice..Thnks

 

[szabi]

You can only erease them with UV light, they aren't EEPROMs.
And since they are OTPs, you can't reuse them.
(EPROM=Electrical Programmable...
EEPROM=Electrical Ereaseable Programmable...)

 

[vedo35]

THANKS SZABI,
I KNOW EPROM AND EEPROM WHAT IS . If u looked to datasheets its writing eeprom thats why i thought something wrong. I will try to erase with UV otherwise going to trashcan

 

[jbeng]

The only EPROMs you can erase with UV are ceramic with a window in the top. Usually, parts like this with numbers that start with 27 either have the window and are UV erasable or have no window and are one-time programmable. (Actually, I think they use the same chip in both versions, but the OTP devices are molded in opaque black plastic with no erasing window.) The part number begins with 28C on most of the (older) EEPROMs I have and 28F on the flash programmable chips.
Jeff

 

[vedo35]

yes true they dont have window. I thought anyway it can erasable with uv light
So better to throw to trashcan?

 

[Analog]

yes true they dont have window. I thought anyway it can erasable with uv light
So better to throw to trashcan?

Actually they CAN be erased. You need to do it with an XRAY machine. Back in the 90's, I had a sales guy take some proto boards overseas and he had them xrayed before his flight. I was using windowless OTP devices. Needless to say, they were erased when he got to Europe. So much for that.

Xrays are at a higher energy than UV, and they do just as good a job of bleeding off the charge on the EPROM transistor. So there you go.

 

[jbeng]

I hadn't really thought of that, as most folks don't have an x-ray machine available to use. As luck would have it, our company has 2...
Jeff

 

[szabi]

I think this is very interesting!
I'm wondering if OTP PIC's can be (ereased) reprogrammed this way?

 

[vedo35]

Xray idea is very interesting. But the problem where can i find the xray light. I dont think if i go to hospital and wants from doctors can u also erase of my this eeprom for me with your xray machine. Or whose they will make rontgen film and can you hold at your otoher hand of my eproms
So i am not throwing them. Maybe one day i can find xray somewhere.

 

[Sceadwian]

Check any local electro plateing shop, any one of them worth anything will have an x-ray machine for thickness and composition determination. Just ask them to shoot the window for you.

 

[szabi]

I left a PIC16C74 in an Xray machine (my mom works in an institute of cardiovascular diseases) over 1 minute, and nothing happend. So mith is BUSTED.

 

[Analog]

I left a PIC16C74 in an Xray machine (my mom works in an institute of cardiovascular diseases) over 1 minute, and nothing happend. So mith is BUSTED.

It depends on the intensity of the xrays. An xray through your body needs to be very light, so as not to mutate your cells into cancer. An xray machine at the airport is another matter altogether.

I should amend my previous statement to say that the OTP eprom wasn't totally erased, but enough bytes were fubared that it was rendered useless.

 

[jbeng]

Another problem with using an medical x-ray unit is that the exposure time is pretty short. You'd probably need to use an industrial machine in which you could switch on the tube and leave it on a while. Also, it's intensity would probably be much higher (especially if it was used to x-ray welds). Szabi said that he left his rom in the machine for over a minute. Was the x-ray tube on for that entire time?
Jeff

 

[szabi]

Yes, it was on all the time. It has a foot pedal that needs to be pushed to work.
Another thing is, that the chip is code protected, so I'm not 100% sure if there was actually any erasure, because the CP fuse remained on. So I wasn't able to see any changes in the program area.