EPROMS ?

[Mr.collection]

I know what they are but I read some where that they erase themselves after 25 years. I can't find where I read it but I am sure you guys would know. I know it was with a bunch of text with info on how to erase them with UV light but it may have been a different kind of ROM chip they were talking about.

Thanks

[kyuusaku]

EPROM don't erase themselves. Bits are prone to "bit rot" phenomenon but I don't believe the situation is as urgent as many will have you believe. The same thing goes for uncovered windowed EPROMs. It's possible for sunlight to reset bits but unless you leave the ROM in direct sunlight for extended periods of time, you shouldn't have anything to worry about. Nevertheless, I would suggest backing up any ROMs that are important to you since it's always possible for them to get damaged electrically rather than corrupted.

[calvinthedestroyer]

As an Electronic technician I would agree. If your EPROM dies after 25 yr's of service then it has lived a full life.
I have also heard that a flash from a camera will erase an un-covered EPROM.

[calvinthedestroyer]

I have heard that used Eproms (that were used then erased and then re programed) can become faulty because the old program can grow back on the chip.

Another person said that this can be fixed by erasing the eprom twice.

One thing that I would like to know is how do you make a 27c512 eprom look like a 27c064 eprom? Since 64k eproms are getting harder to find.

[tokumaru]

One thing that I would like to know is how do you make a 27c512 eprom look like a 27c064 eprom? Since 64k eproms are getting harder to find.

Just connect the higher address pins to +5V or GND. This will make it possible to only read the same 64k all the time. To address 8KBytes (64kbits), 13 address lines are needed (A0 through A12). These should be connected normally, while the higher A's should go to +5V or GND.

[MottZilla]

I read an explanation once about EPROMs which was something like this. Each Bit in an EPROM is like a room with a tiny door. When you erase the EPROM you pack every room with people. When you program the EPROM you are using the programming voltage to push people out of the rooms. The EPROM decides wether a bit is 1 or 0 based on the number of people in the room. So over a long time, it's possible for the contents of these cells to change and cause a bit to not be what you intended and in program code this could be fatal.

Erasing EPROMs twice may work for some, but I've heard it's possible you can over-erase them and cause memory cells to be fucked up for good.

You should just use the recommended erasing process by the manufacturer or someone experienced. Either way you shouldn't use EPROMs for long term storage. They aren't meant to last forever. If you want something that last longer I believe FlashROM would be what you want. Another thing you may want to do is install a socket so if the programmed EPROM goes bad you can more easily replace it. If you are doing development you'll definitely do this.

[kyuusaku]

There's no such thing as cells in an EPROM, each bit's state is determined by a fuse. If the fuse is set (during the erasing process) the output is 1, if the fuse is blown (during the programming process) the output is 0.

I'm pretty sure EPROM is a lot more stable than Flash since the whole basis for Flash is that something's in an indeterminate state. EEPROM and Flash are a lot closer to your analogy.

[MottZilla]

Maybe I had that confused and the thing I read was about EEPROM.