# Can an EEPROM be one-time-programmable?

I'm confused, and I hope you can help me figuring out, what I misunderstood. I am not an electronics engineer, so bear with me :)

I have a chip, from the engine control unit of a Toyota Yaris Verso from year 2000, with the following print:

ATMEL010
25020NB
9D3203C


I have not been able to find a datasheet. And that really surprises me. I did find one for At25020B, but not for one with the NB suffix. Why would Atmel make a chip and not publish the datasheet?

First of all, from what I can find, the Atmel AT25 series are all EEPROM (source). So this chip should be an EEPROM. Am I right?

I looked up, what the suffices mean and found the following (source: Explanation of Atmel’s Part Number Code). B means some kind of military compliance. The N says something about the package:

N = Leadless Chip Carrier, One Time Programmable


I think the N in some cases mean "Leadless Chip Carrier" and in some cases "One Time Programmable", since they are not related. Do you agree?

Looking at the picture, it obviously has 8 leads, so it is not leadless, and thus N must mean one-time-programmable. Do you agree?

As far as I understand the EEPROM technology it is by definition erasable/rewritable.

Is this really a one-time-programmable (and therefore not erasable/rewritable) EEPROM? Or what have I misunderstood? :)

The background for even asking is because I have not had luck with communicating with the chip. A friend, who is an experienced tingler tried to with Bus Pirate and command line tool flashrom, without luck.

• Why would Atmel make a chip and not publish the datasheet? Oh, that happens a lot! Open some old (1970s) Hewlett Packard measurement equipment and there you can find many chips with HP part numbers on them. Often they're very jellybean chips (common chips everyone uses), these just get a special number after packaging. If you buy enough chips you can have a smiley printed on them as well if you like. – Bimpelrekkie Oct 6 '18 at 12:23
• The other discrepancy here is one that you don't seem to have noticed: according to the datasheet for the At25020B, the SOIC version has an abbreviated part number marking of "52BL", not a full part number. I wonder if the part was produced using an older numbering scheme that has been replaced... – Jules Oct 11 '18 at 15:56
• ... hold on, when you say the chip came from a "Toyato 2000 engine control unit", does that mean from a vehicle manufactured in 2000? Because the nearest I can tell, the At25020B was introduced in 2010. – Jules Oct 11 '18 at 16:03
• Yes, it was produced in year 2000. I changed the text to make that clear. – Mads Skjern Oct 12 '18 at 14:46
• Sorry, but I don' t think I understand what you mean with the abbreviated and full part number. Maybe that is the key to understanding the reply I got from Atmel. Please see my answer with the information I got from Atmel. – Mads Skjern Oct 12 '18 at 14:50

I did find one for At25020B, but not for one with the NB suffix. Why would Atmel make a chip and not publish the datasheet?

Why wouldn't they?

Chips are often manufactured for specific customers with specific needs, especially if the numbers are large enough.

Probably, though, your IC is an AT25020 of some kind, which pretty much sets the way it communicates.

I think the N in some cases mean "Leadless Chip Carrier" and in some cases "One Time Programmable", since they are not related. Do you agree?

No. The wording strongly suggest it's a leadless, one time programmable part. Not either. Both.

Looking at the picture, it obviously has 8 leads, so it is not leadless, and thus N must mean one-time-programmable. Do you agree?

No, it seems that naming scheme simply doesn't apply to the IC you have.

As far as I understand the EEPROM technology it is by definition erasable/rewritable.

Wikipedia: EEPROM stands for Electrically Erasable Programmable Read-Only Memory; so yes, by definition, it's electrically erasable. That functionality is controlled by an on-chip erase controller. If you simply disable that after the first write (e.g. by automatically burning a fuse), then it becomes one-time programmable.

Remember, you do not directly interface the memory cells with the pins of your IC; you talk to some kind of controller that takes the messages ("hey, can you give me data from address 0xDEAD?") and interacts with the actual memory based on its own discretion;.

The background for even asking is because I have not had luck with communicating with the chip. A friend, who is an experienced tingler tried to with Bus Pirate and command line tool flashrom, without luck.

What's the chance of that IC simply being broken?

• Thanks for the great elaborate answer. Yes the wording suggests that N implies both. But I just find it strange if all leadless should be otp and vise versa. If you look in the document, there is no letter other than N to imply leadless, and no letter other than N to imply OTP. So IMO (again, as a layman) common sense implies that N implies "either". – Mads Skjern Oct 6 '18 at 18:53
• The keys were lost. I need to write a new immobilizer key to this chip. The ECU was working beforehand, so I think the chances of it being broken now, after we removed the chip, is very small. But I cant say for sure. – Mads Skjern Oct 6 '18 at 18:55
• I find it strange that you're so hung up on that document. That document clearly doesn't apply to your device. And seriously, English isn't my first language, but my interpretation of "Letter N: a, b" is that "N" implies both "a,b", like it would everywhere else. – Marcus Müller Oct 6 '18 at 19:09
• Your comment does not address my arguments. However, since you are so certain and since I have little electronics insight, I expect that you are right on this matter – Mads Skjern Oct 6 '18 at 21:58

OTP is useful for anything that can't or shouldn't be re-programmed. Manufacturers might want to use it to prevent tampering or misuse by the public or for other reasons. You might want to use it for a bootloader so that a device cannot be "bricked" by a bad firmware update (assuming the firmware resides on eraseable memory).

Any application where true mask ROM might be used is a good candidate for OTP. Compared to mask ROM, OTP allows the manufacturer to optimize the product development schedule by finalizing firmware AFTER the hardware design is complete, and it allows for firmware changes to be rolled into production with less lead time than mask ROM.

OTP is typically less expensive than similar forms of memory which can be reprogrammed many times.

Sometimes chip manufacturers make custom parts for large volume customers. The large volume customer does not want the datasheet for the part made public. This is somewhat common.

To answer your question more generally, most modern EEPROMs have OTP (one-time-programmable) areas and/or the ability to "lock" the data within the general area. The precise features available depend on the specific chip, and will be detailed in the datasheet.

Many EEPROMs also have protection against accidental erasure or reprogramming, usually according to a JEDEC standard which requires a particular command sequence before the actual erase/write command. Erasure must occur before reprogramming in any case, due to the way flash memories work. Some small EEPROMs include an erase cycle in their programming instruction, so don't need a separate erase instruction.

In the specific case of the AT25020B, there's a pair of nonvolatile write-protection bits in the status register, an external write-protect pin and a write-enable prefix instruction. Use the "read status register" instruction to determine the state of the write-protection bits. To change the write-protection bits, you must hold the /WP pin high, issue the "write enable" prefix instruction, then issue the "write status register" instruction; a zero byte should clear the protection on the main array.

I have not been able to find a datasheet.

• Good find ... although you should probably add to the answer the fact that the datasheet indicates the 'N' suffix is for a temperature range variant (-40C to 85C, versus -55C to 125C for the standard version). – Jules Oct 12 '18 at 1:30
• A bare link does not really constitute an answer within the guidelines of EESE. At an absolute minimum your answer needs to include an explanation of what information found at the link resolves which uncertainty of the question. This must be of a form which continues to have lasting value even if the link dies. – Chris Stratton Oct 12 '18 at 3:34

Others have answered thoroughly about the overall question; if an EEPROM can be OTP. But I want to add, what I found out about this particular chip. I wrote Atmel and asked for the datasheet, and they were very helpful. This is the response I got:

The complete part number of the device is AT25020N-10SI and it is made in 2000. The 9D3203 wafer was made in 1999. That device contains Pb (lead) and therefore is not RoHS 6/6 compliant. f This device is the first generation AT25020 device and was EOL'd by PCN SC030403A that introduced AT25020A. The AT25020A was EOL'd by PCN CC084205D that introduced AT25020B.

AT25020 has 10ms maximum write cycle time. AT25020A and AT25020B are 5ms maximum write cycle time.

AT25020 may not operate in AT25020A or At25020B sockets due to this difference.

I don't know why they would produce this chip with a print other than "At25020", which they call "the full part number".

• Thanks for following up. It's too bad this doesn't explain why you seemingly have not gotten even read operations to work, or have you now had success with those? – Chris Stratton Oct 12 '18 at 14:46
• I dont have skill nor equipment to do it on my own, but I will try soon again with a friend, who perhaps can make use of this new information. I will write an update. – Mads Skjern Oct 12 '18 at 19:11

OTP (One-Time Programmable) is a very cheap IC because it can be only programmed once (that is the one-time), for this reason this the price point is much cheaper than a flash IC (which requires more floor plan).

Try to get the vendor's datasheet and see how this device communicates (some are serial output others parallel).

• This seems to say pretty much the same thing as your previous answer. You should edit the previous one and delete this unless you deliberately want to give two different solutions to the original question. You could improve the appearance and legibility of your posts by using proper sentence structure, punctuation and spacing. – Transistor Oct 11 '18 at 18:19
• @Greenonline please don't make trivial edits which needlessly bump answers that are low quality due to irreparable problems with their information content to the top of the queue. – Chris Stratton Oct 12 '18 at 3:29
• This is a very poor answer. The question is not about flash, it is about EEPROM. OTP, which is merely speculation, if in fact reality in this case would not be a cost savings, it would be an immutability feature. – Chris Stratton Oct 12 '18 at 3:36