Image of circuit, the i/o pins also have jumper wires that I connect to VSS/Ground for inputting dataI have a 28c256-25 EEPROM that I have created a breadboard circuit to program. The datasheet says after the address is set and the data is put on the I/O pins, a low pulse on /WE while /OE and /CE are tied high should write that data into the provided address.
I have tried (using an RC circuit) giving a 33 nanosecond, 100 nanosecond, and 500 nanosecond negative pulse on /WE, but I could not get the data on the I/O pins to get written into memory. Here is the datasheet: https://www.jameco.com/Jameco/Products/ProdDS/74878XICOR.pdf There is a short description of the Write cycle on page 4 and a timing diagram on page 14.Am I supposed to send the data on the I/O pins during or after the /WE pulse or something? What am I doing wrong?
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4\$\begingroup\$ A schematic would go a long way towards helping us solve this. \$\endgroup\$Adam Lawrence– Adam Lawrence2020年06月09日 20:46:32 +00:00Commented Jun 9, 2020 at 20:46
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\$\begingroup\$ I have added a schematic. It excludes the jumper wires that I would have on the breadboard on the I/O pins that I plug to VSS/Ground to pick what data I want to write. \$\endgroup\$Yigit_Yildirim– Yigit_Yildirim2020年06月12日 03:28:27 +00:00Commented Jun 12, 2020 at 3:28
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\$\begingroup\$ Some questions you might like to ask yourself: Is the EEPROM a new part? If it has ever been programmed using the software locked method, you will not be able to write to it using the hardware method you are using. Also, are you sure that your write pulse is really below 0.8V (VIL) for the required TWP period of 100ns? How are you applying the Data to the I/O pins - that does not seem to be shown on the schematic. \$\endgroup\$elchambro– elchambro2020年06月12日 03:41:59 +00:00Commented Jun 12, 2020 at 3:41
3 Answers 3
As per your description, you keep /CE high and that keeps the whole chip disabled. /CE must be low to enable read or write operations.
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\$\begingroup\$ I accidentally wrote that, sorry. /CE is low and it still doesn’t work. \$\endgroup\$Yigit_Yildirim– Yigit_Yildirim2020年06月10日 21:50:22 +00:00Commented Jun 10, 2020 at 21:50
I had to use an RC delay of 680ns to write to a new 28c256, as per the Ben Eater videos on youtube. Then it worked perfectly programming by hand.
Get rid of R21 - /CE must be LOW to make chip enabled. You don't need any specific pulse to write a data in your setup. Just pulse negative the /WE with a push button and don't think about nS specifications - it counts when you switch it fast with a microcontroller. It works perfect, did this many times.