On Sun, Jan 25, 2004 at 05:46:54PM -0800, steven wrote:
> My first attempt at the so-called killer poke on my
> Commodore PET 2001-8 resulted in a 30% speed increase!
>
> I used "POKE 59458,62"
>
> No smoke, either!
That's because it's a 2001-8. The old, TTL video PETs used that POKE
to, in effect, let BASIC "ignore" the vertical blanking interrupt. In
essence, the ROM routing for PRINT checks the VBI and only fiddles with
video memory when the beam is off. That's why directly manipulating
screen memory in machine language was always faster.
The problem came with _later_ models than yours. IIRC, the effect of
the "killer poke" was to change the direction of a bit in a PIA or VIA
from an input bit to an output bit. The consequence of that is, with
one of the later models with a different video circuit, a totem-pole
transistor arrangement was permanently engaged and one of the transistors
was overdriven and smoked.
-ethan
--
Ethan Dicks, A-130-S Current South Pole Weather at 26-Jan-2004 08:20 Z
South Pole Station
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Ethan.Dicks_at_amanda.spole.gov http://penguincentral.com/penguincentral.html
Received on Mon Jan 26 2004 - 02:33:12 GMT