Re: PET 2001/2001N can "write" to ROMs

Den Tue, 23 Apr 2019 06:22:33 +0200 skrev Gerrit Heitsch
<gerrit_at_laosinh.s.bawue.de>:
> On 4/22/19 10:14 PM, Francesco Messineo wrote:
> > Hi all,
> > Ok, the subject is a pun, but write is in double quotes anyway. I
> > was wondering why the PET (at least the 2001 and 2001N, the ones I
> > have), leave the ROMs selected during a write cycle on ROM space.
> > This of course makes a data bus contention because the selected ROM
> > will drive the data bus and the 6502 will drive the data bus too
> > since it's on a write cycle.
> > I wonder if this can be a factor in the high failure rate of the old
> > 6540s and the newer 2332/2316.
> 
> No, NMOS outputs cannot be damaged if they work against each other.
 
Somewhere I read about copy protections for C64+1541 that let the 1541
write to ROM more or less contiguously if the software thought it was a
pirate copy, and this apparently damaged the ROMs.

Not sure which process those ROMs were made of though.


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