Odd flash behaviour

From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2003-01-25 20:18:28

Hi all,

I have made some experiments with the VIC-20 cartridge prototype, which
only has 512 kilobytes of flash ROM.  I've started writing a flashing utility
that can successfully clear the chip.  (I've verified it by reading 8
kilobytes of $ff from the chip.)

However, when I program 8 kilobytes of the chip (that would be random
locations in the chip, since I have shuffled the address lines to simplify
the circuit board), some bytes that should be $ff are instead $fe or $fd.

The embedded programming algorithm in the chip does not report any errors,
and my program also checks that after programming a byte, it must read back
the same within 256 retries.  I also tried a modification that would skip
any $ff bytes, but it didn't change anything.  All other bytes than these
$ff's are programmed correctly.  Has anyone else had similar experience?
Any ideas or suggestions?

The next logical step is to read the whole chip (off the system) and check
if the remaining 512-8 kilobytes of the chip are $ff, as they should.  I
hope they are, since anything else would indicate a hardware problem.


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