at28c256 write protection

[DavideRuzza]

hi. i have a problem to program the at28c256 eeprom. with the at28c16 works perfectly . I have read in its datasheet that there is a write protection to unlock with a sequence of byte in some registers.
I have tried to write this sequence with the library write function, but it did't work

[levvayner]

Hi David, I am having the same problem with a different set of code and differently built programmer. I bought some AT28C256 on eBay, and spent a long time trying to figure out what was wrong with my code/wiring. Long story short, your problem might be the same. If no matter what you do, you are getting 0xFF back, you might not have genuine ATMEL AT28C256 chips, rather something that was "rebranded" in China, even though I bought mine from a U.S. seller.

More here http://stardot.org.uk/forums/viewtopic.php?t=11039

[MeadeRobert]

So... if the chips aren't genuine... we're out of luck? I bought 5 from jameco and 2 from amazon. I can't get any of them to program. I just went out of my way and bought and EEPROM programmer from amazon. I'll let you know if its chips or this setup.

[DavideRuzza]

Sorry if i haven't reply. I have to say that i managed in some way to make it work but only for a few times. With the code of Ben Eater's programmer i manually set the addresses like the datasheet said to remove write protection. I was surprised but it worked, infact i programmed it a few times. Than i removed the chip from the prototype board where i built my diy programmer to see the data from another circuit. When i put the chip again in the programmer it had not worked anymore and i gave up. I buoght the atmel28c16 which worked perfectly but i had to renounce to all that storage size that the Atmel 256 offers 2018-05-18 10:35 GMT+02:00 Robert Meade <[email protected]>:

…

So... if the chips aren't genuine... we're out of luck? I bought 5 from jameco and 2 from amazon. I can't get any of them to program. I just went out of my way and bought and EEPROM programmer from amazon. I'll let you know if its chips or this setup. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#5 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AdPQbLwuShhJlrP46vvezoyZfYMUEWf8ks5tzofLgaJpZM4RlyUw> .