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Problem with writing eeprom memory

Novacicm

Aug 12, 2017
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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?
 

Novacicm

Aug 12, 2017
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kellys_eye

Jun 25, 2010
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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.
You will - a standard 'unprogrammed' EPROM is usually set to FF (all locations).
 

Novacicm

Aug 12, 2017
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You will - a standard 'unprogrammed' EPROM is usually set to FF (all locations).

Yeah I know that but also when I try to write memory to some pattern of 8bits I am always getting FF all ones in memory.
 

kellys_eye

Jun 25, 2010
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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.
If you have tied all address and data lines to zero the programming function (assuming you get the proper 'low' pulse applied) will write whatever you have set on the data lines to the address you have on the data lines.

Assuming all lines are zero then the programming pules should write 00 to address 0000.

Have you got pull-up resistors on address/data lines?
Have you got proper supply line decoupling in place?
Have you got a de-bounced program signal?
 
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