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

On Tue, Apr 23, 2019 at 6:23 AM Gerrit Heitsch
<gerrit_at_laosinh.s.bawue.de> wrote:
>
> 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.

Ok, what about a 27Cxxx EPROM or 28Cxx EEPROM against the 6502 data
bus? It's a possible replacement (with adapters) for original ROMs or
it can happen in a RAM/ROM daughterboard.

Frank