compucolor HCF

[Heinz Wolter]

when I was in high school (teaching the grade 9 class, not taking it)
- one kid got to pay the repair bill on the Commodore PET.
One magic poke to the 6845, and PPPPFT! there goes the monitor cicuitry;)
But thwen again, random pokes to random locations will cause havoc...
The real (blue) screen of death! (monochrome 40 col. version)
h

Liam wrote:
> > This is not as rare as you might think. Several machines -- the IBM PC
> > MDA card + 5151 monitor, for exampe -- suffer from this. There is no
> > horizontal oscillator chip in the monitor circuit, the line output stage
> > (horizontal output stage) is driven from the signal produced by a
> > software-contorlled IC (in the case of the MDA card, it's a 6845).
> > Mis-programming that does just what you said....
>
> Aha! The famed HCF instruction? :¬)