5PCS AT28C256-15PU EEPROM IC Parallel 256K-bit 28-Pin DIP-28 NEW

These EEPROM's were used in a 1802 retro-computer and worked perfectly. They met spec's and I was able to program and erase and re-program them with no problems.

I noticed there were mixed reviews of this batch of 5 28C256 EEPROMs. I figured if I was able to get at least 2 good ones, I would break even compared to getting them brand new from somewhere like Jameco.I have the TL866 II Plus EEPROM Programmer so any of them being software lock wouldn't be an issue. Software lock is not for code protection but rather to prevent accidental writes during circuit power on sequences.With the programmer, every one of them passed verification for all FF, all 00 random bytes, and programming images for the Ben Eater Worst VGA adapter ever.However only 2 would display properly in the VGA project. I can't really fault these ROMs as the project is demanding much faster response than the datasheets guarantee, with monitor pixel clock at 25nS and address lines changing at around every 100nS.We'll see how reliable all 5 are when I use them in the 6502 project instead, which clocks at 1uS.Packaging could be better as some have said. It was double-bagged in antistatic bags, then shipped in a padded paper shipping envelope which could have gotten the pins bent during shipping. Fortunately they weren't and they did look new.

All 5 of my chips were readable and writeable with no issues, contained no original data, and could be erased without any problems. Successfully used to ROM swap a Nintendo cartridge.

These work great.

~ My complete order delivered was wrong.~ I ordered AT26C256-15PU~ All chips sent were the wrong & obsolete type, AT28C256-15PC & AT29C256-90PI, besides two being used, faded, & scruffy.

All were good. Great price. However three of them were software locked, showing hex FF for all bytes and unwritable. You have to run the unlock sequence in the data sheet and the timings are fairly strict. A 90us delay between each write in the 6 byte sequence works for me. Too much faster or slower will NOT work. FYIDatasheet for the AT28C256 is available all over the web.

I ordered 1 set and 1 of the 5 chips erased successfully but refused to write, all others took a full random write and seemed to work fine. Amazon sent a replacement set of 5 and 1 of those 5 identified has having 3 bad pins in the reader (Attempted multiple times). All of the chips came with different contents on them and not in any consistent pattern. So maybe they're salvage or chips rejected from quality control? Packaging was also not the best. But for the price of them I can't complain too much aside from the hassle of dealing with the return.

The IC are not new. Out of five one was dead. They should not be labelled as new - all contained some code. Still a good deal - new are ~$9 apiece