Unable to write to eeprom at28c256 HELP PLEASE

[Novacic]

I am trying to write atmel at28c256 on breadboard so I tied all address lines to ground, and all I/O lines also tied to ground. I untie I/O lines for reading, tie 'WE to high, 'CE to low, and 'OE to low for reading. I am reading all ones at I/O ports, no matter what address. So, when I try to write this eeprom I put 'OE high and with 'WE line I touch to ground so that should write stuff to memory but it does not, all I/O ports were connected. I also made small RC circuit with button on WE but that also does not work. Any toughts?

[slambo511]

Hi,

I am no expert myself but am in a similar position, I found this video



very helpful - he uses the 16k version not the 256k one you have but they should have the same pin out. Hope it helps.

[David Hess]

-OE must be high, and -CE and -WE must be low to start a write cycle.  The falling edge of -CE or -WE latches the address and the rising edge of -CE or -WE latches the data and starts the write cycle.  -CE or -WR must be low for at least 100 nanoseconds.

[jfigge]

I know this is old, but wanted to post a response incase someone, much like myself, stumbles across this post while looking for answers...

It seems some 28C256 EEPROM chips are being shipped with SDP (Software Data Protection) enabled.  Technically Atmel doesn't ship the chip in this state, so it does make me wonder if my branded chip is a clone 

Anyway, when I wrote the code to program the chip via a Nano I found I wasn't able to write to the chip, nor issue the required commands to unlock it.  I 'believe' the problem was because the code I original wrote ran WAY too slowly to be able to send the unlock commands within a single page (bytes must arrive within 150us to keep the page going).  Once I figured this out I re-wrote the code to use port manipulation and we able to remove SDP and update the EEPROM.

Here's my code: https://github.com/jfigge/arduino-28c256-programmer

Good luck, and this comes with no warrantees (but is free to use and abuse )

[wraper]

so it does make me wonder if my branded chip is a clone 

Recycled e-waste, and likely relabeled. Just date code and/or speed grade changed or even chip from another manufacturer relabeled.