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Homemade EEPROM Programmer Issues

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ziptol:
Hi,
I've recently been working on making an EEPROM programmer using an Arduino Mega 2560, and have run into a roadblock. I am attempting to program an AT28C256. After hooking up the EEPROM and running my program, which currently writes to an address than reads from it as a test, no matter what I write, I always read 11111111 (0xFF).

At first I thought it was an issue with my program or connections, but after checking all of the elements of the program and double checking all of my connections, I decided to try it on a HM62256LP-70 RAM chip, which has the same pinout as the AT28C256 and, as far as I can tell, the same timing. When I did this, it worked perfectly. At this point, I assumed that I had broken my EEPROM at some point and ordered another one.

Today, I got the EEPROM, plugged it into my "programmer" and ran the program, only to get the same issue I had with my first EEPROM.  |O 

At this point, I have no idea what the issue could be, would be very grateful for any troubleshooting advice someone can offer me, and am happy to answer any questions.

AT28C256 EEPROM Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/doc0006.pdf
HM62256LP-70 RAM Datasheet: https://www.futurlec.com/Datasheet/Memory/62256ALP.pdf
Arduino Code is attached.

Thanks All!



mikerj:
Are these new parts from a reputable supplier?  Are you waiting sufficient time for a write to complete (or polling the status bit) before trying to read back the data?  Is the supply voltage to the part definitely remaining above the write lock-out voltage during the write operation?  Have you tried disabling the software data protection (though shouldn't be enabled on genuine new parts)?

ziptol:
1. The parts are all supplied from Jameco, which, to the best of my knowledge, is reputable.
2. After the write operation, the program waits 10ms before continuing, which should be well after there would be a problem with reading.
3. The supply voltage is remaining at around 4.85V, which is within the 10% tolerance of 5V of the AT28C256.
4. I just did the write operations to disable SDP, with no luck. The part, as far as I know, is new.

Helix70:
I am not sure, but it doesn't look like you are handling CE as per the datasheet (or at all for that matter).

ziptol:
I’m holding CE low in hardware

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