One time programmable *EPROMS* ? wtf? - Page 1
Forum section: electronics / projects

author: huiewhdwiuef
author_rank: Newbie
timestamp: September 18, 2020, 10:35:13 pm
content: I got an AT27C020 EPROM thinking I got an Erasable Programmable Read Only Memory, it was advertised as an EPROM but now I see on the datasheet it's one time programmable. wtf?https://media.digikey.com/pdf/Data%20Sheets/Atmel%20PDFs/AT27C020.pdf

author: wraper
author_rank: Unknown
timestamp: September 18, 2020, 10:37:43 pm
content: WTF you are surprised by that. It's basically an UV erasable EPROM but in cheap plastic package without window so cannot be erased. Electrically erasable is EEPROM, not EPROM.

author: huiewhdwiuef
author_rank: Newbie
timestamp: September 18, 2020, 10:39:30 pm
content: oh fuck right.should they be called eproms though? isn't it misleading?The die is the same though, idk...

author: wraper
author_rank: Unknown
timestamp: September 18, 2020, 10:46:22 pm
content: PROM naming without E was used only for memory with burnable fuses on the silicon die, not types storing electric charge.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 18, 2020, 10:49:07 pm
content: OTP devices have only been around for about thirty years.That must be a very large rock you’ve been hiding under

author: huiewhdwiuef
author_rank: Newbie
timestamp: September 18, 2020, 10:57:26 pm
content: well if i decap a chip it's gonna be one of the firsts in the list

author: richard.cs
author_rank: Super Contributor
timestamp: September 18, 2020, 11:06:57 pm
content: You can erase it with x-ray or gamma. :-)But you probably shouldn't.

author: huiewhdwiuef
author_rank: Newbie
timestamp: September 18, 2020, 11:23:09 pm
content: interesting but yeah, a bit impracticalout of curiosity, do you think a medical x-ray machine would do they trick ?Edit: I don't think so, i would hope the dose a human gets cant just wipe an eprom

author: Stray Electron
author_rank: Super Contributor
timestamp: September 19, 2020, 03:14:25 am
content: Quote from: WattsThat on September 18, 2020, 10:49:07 pmLonger than that. I used to have an Intel 1602, the OTP version of the 1702 Eprom. IIRC the date code on it was 1973 or 74. IIRC it was the only one that I ever saw and it was only listed in the first edition (1972 I think) of the Intel data book. Intel's plan was that people would use EPROMs to develop their SW and then use OTP Proms in mass production but it turned out that the OTP versions weren't significantly cheaper that the Erasable version so almost no one bought them and Intel quickly dropped them from their product line.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 19, 2020, 03:53:44 am
content: I understand x-rays can be used to erase them, but it takes a substantial dose, and causes much more damage to the chip (maybe 10 erase cycles, if that, versus many thousands for UV).Think about a UV lamp, being about the brightness of a pen light, but at UV. Now imagine that intensity, but in the x-ray band at 1000 times the energy. Now imagine that for ten minutes. That's one hell of an exposure! (No, it's not photon-for-photon, there's a dividing effect at work so you need much less intensity for the same exposure. Probably, like, 1/100th the intensity, or something. Still, that's comparing a pen light to an LED flashlight. But still, a common medical x-ray might be equivalent to a dim indicator LED, so the exposure will have to be really long.)(I don't have a clue how much exposure is really needed to do this, but it would be easy enough to test:set up a reader and start exposing!)Tim

author: helius
author_rank: Super Contributor
timestamp: September 19, 2020, 04:31:29 am
content: That's an interesting thought experiment, but there are some issues you'd need to consider if you really wanted to try it.EPROMs are intended to be erased while removed from the circuit and unpowered. If exposed to radiation while powered, there are other effects that can either skew the result or disrupt them completely. One is the threshold shift from amplifier transistors or references being bombarded. This changes the result of reading out a location in the memory, and could also affect the charge stored. You could even have single-bit-upsets from X-rays as they are much more energetic. The other issue is dislocations in the crystal lattice caused by radiation, which are cumulative and eventually raise the "dark current" that makes cells forget their contents.