AT28C64B is locked

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I bought a few types of AT28C64b parallel eeproms. Two of these chips failed to work. One was filled with 1's but any attempt to re-write them with a high-to-low transition on WE failed to program the chip. No matter what the data I put in, it never succeeds in programming the memory. The other chip also suffers the same problem except that it was filled with completely random stuff, as opposed to a usual eeprom that's fillled with all ones in it. I don't know if the chips are already dead or their SDP are disabled by the manufacturer. Any thought is appreciated.

Last Edited: Fri. Jan 12, 2018 - 03:58 PM
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analogrfdsgn wrote:
Two of these chips failed to work. One was filled with 1's.......

That is the 'blank' state....meaning the EEprom is empty.

 

analogrfdsgn wrote:
Two of these chips failed to work. One was filled with 1's but any attempt to re-write them with a high-to-low transition on WE failed to program the chip. No matter what the data I put in, it never succeeds in programming the memory.

Did you have the Chip Enable pulled low, and OE pulled high?

 

Did you use Data Polling to check to see that the write cycle completes?

 

analogrfdsgn wrote:
I don't know if the chips are already dead or their SDP are disabled by the manufacturer.

What does the datasheet say about the SDP?

 

Page 4 of the datasheet:

The SDP feature may be enabled or disabled by the user; the AT28C64B is shipped from Atmel with SDP disabled.

 

You could always send an SDP disable command.  Page 10 of the datasheet explains how to do this.

 

Jim

 

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