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cannot write to EEPROM

Fairface

May 21, 2017
1
Joined
May 21, 2017
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So I tried to build a simple manual EEPROM programmer to program the chips just by switches. I am able to read from the chips (all outputs are 1), but I am not able to write into them by bringing notWE low and than high again (while notOE is high). When I set it to output it outputs all ones at the IO pins as before no matter what I try to program into it. I have tried 3 different EEPROMs with the same results. I have also tried to disable the software data protection, but nothing has changed. I have measured the voltage on all pins few times and it all seems to be fine (voltage around 5,04V). I am using the AT28C256-15PU datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/doc0006.pdf
Has anyone experienced something similar? Any ideas why is this happening?
 
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