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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?

Novacic
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  • Try a write cycle with all IO lines tied to ground. Then untie the lines and do a read at the same address. – WhatRoughBeast Aug 12 '17 at 18:40
  • I already tried this and I still I cant write anything to the memory – Novacic Aug 12 '17 at 18:52
  • Maybe its write protection is on? Please read the datasheet about this. – Janka Aug 12 '17 at 18:56
  • How can I disable write protection on this chips. Btw this chips are brand new shouldnt they be write protect disable as new? – Novacic Aug 12 '17 at 19:05
  • If they are really brand new they should not be write protected. I tried programming an AT28C256 by 'touching' wires to ground on a breadboard (with pullup resistors on /OE and /WR to avoid floating inputs) and it worked perfectly! – Bruce Abbott Aug 13 '17 at 04:47

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