Problem of writting to AT28C256

[ellvel]

I am using AT89C51 to write data into a AT28C256 for data backup. My circuit is designed well (I'm sure that because I tried to replace AT28C256 by 62256 and it worked well) but I can't write data into AT28C256 even I did that successfully 2 years ago. I tried for 5 new AT28C256s but I got the same bad result. So, what is my problem? Please help me! and give me a sample code!

 

[eblc1388]

How did you test it?

If the bit7 of the read data after write is the complement of the written data, then the reason is simple. You have not allowed sufficient time for the chip to complete the EEPROM write cycle after issuing the write command so the chip uses this method to inform you more time is needed.

There is one more catch, the pin I/O 6 will toggle upon successive read operations so you must take this into account when checking for written data immediately after a write operation. All the information is inside the datasheet.

Added: Just find out that user can also enable software data protection on the chip to prevent subsequent data changes. Make sure this feature is not enabled.(New chips are shipped with protection disabled)

 

[ellvel]

Thank

Thank for for help!
I have just found that all of my AT28C256s are bad. I found that because I use a EEPROM programmer to test them. My god, all of them are damaged even I bought them new. So, I will buy some more and try again. I will post the result as soon as I get it. Thank you, again.