RE: In search of bad 4164, 41256 DRAM

>>I was going to suggest that, for testing purposes, you could extend the refresh interval far beyond specification.  That would cause even a good RAM to fail, and, all being well, the failure would be detected and you'd know your test regimen is effective.

That is an idea too and easy to implement.

>>Oops, but wait a sec...  This raises a more general question.  I hope your test regimen doesn't do its test reads too soon, because reading a cell also causes that cell to be refreshed.  IOW, the test isn't fully comprehensive unless you write to a cell, leave it alone for one refresh interval, *then* do a read to verify its contents.

Currently it writes all cells in a nested loop:

For c = 0 to 511
  For r = 0 to 511
//write bit
  Next
Next

So, each row is automatically refreshed as the next column is written. In fact, I turn off the automatic refresh timer while writing.

The read test is similar loop wise and happens after all writes are done. I can add a variable delay here with or without and automatic refresh timer functioning as well.

Jeff Birt