RE: Odd flash behaviour

From: Gideon Zweijtzer (
Date: 2003-01-26 07:41:58

Hi Marko!

With Flash, you cannot exchange all address lines. Depending on the
actual chip you are using, you should leave the sectors in tact, and
program them one by one. This means that you will have to leave the
higher address lines connected un-shuffled. 

I hope that solves the problem. Which Flash are you using? An Am29F040?


-----Original Message-----
[] On Behalf Of Marko Mäkelä
Sent: Saturday, January 25, 2003 20:18
Subject: Odd flash behaviour

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
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
the circuit board), some bytes that should be $ff are instead $fe or

The embedded programming algorithm in the chip does not report any
and my program also checks that after programming a byte, it must read
the same within 256 retries.  I also tried a modification that would
any $ff bytes, but it didn't change anything.  All other bytes than
$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
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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