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

Am 22. April 2019 22:16:57 schrieb Francesco Messineo
<francesco.messineo_at_gmail.com>:

> 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.
> It was just lazyness/cheapness or do I miss something?

My guess is that this was a cost measure. Under the assumption that the
code would not write to ROM there would be no need to decode R/-W.

André
>
>
> Frank IZ8DWF