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Topic: How to change a chip signature? (Read 7327 times) previous topic - next topic

nickgammon

I think someone mentioned this in passing in another post, probably in the last 12 months.

Does anyone know which (probably undocumented) high-voltage or ICSP programming locations you address to change the chip signature?
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More info: http://www.gammon.com.au/electronics

DrAzzy

No idea, I'm very interested in this too.

The Atmel guy I talked to swore up and down that it wasn't possible to change signatures, or other things like that (like the default OSCCAL value, which is what *I* was interested in changing, so I could tune them and have the chip just work (at least at the temperature I tuned it at) without having to have a special bootloader)
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nickgammon

I seem to recall that one of the long-time experts here found a link which showed you could change the signature as "fuse" byte 4/5/6 or something like that, but can't find the reference now.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

mrburnette

#3
Aug 14, 2015, 04:55 pm Last Edit: Aug 14, 2015, 04:58 pm by mrburnette
This device claims to do that:
Quote
UPDATE 2.1X ADDS NEW FUNCTIONALITY!
Send your own fuses and locks trough terminal, talk with chips with broken signature. If you connect terminal Tx pin to PCB Rx pin - manual mode will be enabled automatically. This requires Tx-terminal pin to be HIGH and OUTPUT when idle. It must pull up the 10K pulldown. If this condition is not met, doctor will work in normal - automatic mode.
http://mdiy.pl/atmega-fusebit-doctor-hvpp/?lang=en

afterthought: maybe it claims to be able to update fuses by allowing the Op to bypass the mangled chip signature... not sure exactly what the page is stating.


Ray

bperrybap

Can't you work around it in s/w?
i.e. if using a bootloader patch it to lie to be whatever you want.
If using ICSP, just go patch the avrdude config file to map the signature read to use the same entry as the signature you desire.

--- bill

nickgammon

#5
Aug 15, 2015, 12:18 am Last Edit: Aug 15, 2015, 12:18 am by Nick Gammon
Quote
Can't you work around it in s/w?
Sure. Just wondering that's all. I just thought I remembered it could be done. Maybe I was dreamin'.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

westfw

I've heard rumors of people doing this with "less careful" device programmers.  Occasionally to their own detriment (not being able to change back?)  But I don't think I've ever seen any actual documentation that says "this undocumented command with these arguments can be used to to set xxxx"  Sigh.

http://www.eevblog.com/forum/microcontrollers/how-bloody-hard-can-it-be-to-program-an-avr-chip/135/

dmjlambert

Well the page for that link further links to this page:
http://www.avrfreaks.net/comment/165666
There is a description of erasing and re-writing signature of tiny13.  Interesting.

nickgammon

Quote
The method employed for this was brute force; I had a program fire off one random sequence after another, checking the chip state after each sequence
I could always try that, I suppose. :)
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

DrAzzy

#9
Aug 15, 2015, 09:31 am Last Edit: Aug 15, 2015, 09:31 am by DrAzzy
NEATO!

Gotta try that...

I wonder if the command is the same on other chips...
ATTinyCore for x4/x5/x61/x7/x8/x41/1634/828/x313 megaTinyCore for the megaavr ATtinies - Board Manager:
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Coding Badly

#10
Aug 15, 2015, 09:44 am Last Edit: Aug 15, 2015, 09:45 am by Coding Badly
Quote
I think someone mentioned this in passing in another post, probably in the last 12 months.
I did.  The signature row is just a bit of Flash.  There is an undocumented pair of serial (ISP) commands for reading / writing.  I remember them being a logical extension of the commands to read / write the program Flash.  I believe I found three references.  I know one was on avrfreaks.  If you want a hand finding the material just let me know.

Quote
The Atmel guy I talked to swore up and down that it wasn't possible to change signatures...
If you ever meet him in person give him a good solid slap for lying to you.


nickgammon

Quote
I remember them being a logical extension of the commands to read / write the program Flash.  I believe I found three references.  I know one was on avrfreaks.  If you want a hand finding the material just let me know.
Yes, please. I think you gave more details last time. ;P

My Googling has just revealed a lot of nonsense about how you can disable the signature checks, not how you can change the signatures.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

Coding Badly


Uh oh.  I fear I did not save a reference...
http://forum.arduino.cc/index.php?topic=318215.msg2203467#msg2203467

Going to have to put on my Google wishing cap.




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