Re: Two new PRGs

From: Olaf Seibert (
Date: 1998-02-16 18:39:26

From: (Andre Fachat)
> I am in the process of exending the VICE xpet emulator to emulate differe=
> nt
> PET models. So far 3xxx-8032 are working. The 2001 ROM seems to break
> the IEEE488 emulation, but I didn't have time to look at it at all so far.
> (I thought about a different EOI line, but first investigation didn't sup=
> port
> it so I need some more time)
> If possible, I would like to have a copy of those ROMs too, to check them
> on the emulator.

The 2001 ROMs have a known bug in this department. When scrolling the
screen, it blanks it by setting some output pin (to avoid snow?). The
same pin is connected to the IEEE EOI line. Perhaps this is what you're
running into.

Later models (the 30xx ones) didn't have the screen blanking feature,
but the ROMs still used it as if it did exist. If I recall right it
was only properly fixed in the 4.0 ROMs.

And then there was the "fast print poke". The printing routines only
put characters in the screen during the vertical retrace. An input
bit somehere indicated this condition. This poke turned the line into
an output, so that printing would go much faster. On older machines
it produced snow, too. On some machines it didn't work, caused weird
screen output, or just plain destroyed them. I have seen the first two
things but never the last.

> Andre
___ Olaf 'Rhialto' Seibert  rhialto(at)   "I would be dead in
\X/ a week if I didn't do /something/. I'd be splattered all over the walls."

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