Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!hc!lanl!unm-la!unmvax!nmtsun!caasnsr
From: caasnsr@nmtsun.nmt.edu (Clifford Adams)
Newsgroups: comp.arch
Subject: HACF (was Re: Risky instructions)
Summary: More fun with BASIC
Keywords: history, pc, PET
Message-ID: <932@nmtsun.nmt.edu>
Date: 13 Aug 88 21:24:07 GMT
References: <5458@ecsvax.uncecs.edu> <1876@looking.UUCP> <753@applix.UUCP> <5440@june.cs.washington.edu> <1239@ficc.UUCP>
Reply-To: caasnsr@nmtsun.nmt.edu (Clifford Adams)
Organization: New Mexico Tech, Socorro NM
Lines: 28

In article <1239@ficc.UUCP> peter@ficc.UUCP (Peter da Silva) writes:
>If anyone out there has a Compucolor-2 (a Z-80 based PC from the early
>'80s) you can implement HACF from Basic:

>10 FOR I = 1 TO 255: OUT 6,I: NEXT

	An even shorter sequence was possible on one model of the
Commodore PET personal computer.  All that was needed was to place a
certain value xxx into memory location yyy.  Several hours later one
of the video chips would be dead.

	The instruction was:    POKE xxx,yyy

	Apparently the value yyy would put the chip into an adjustment
mode, which increased the frequency of a certain function.  Faster and
faster.....till meltdown.

	What was really interesting is that COMPUTE! magazine (back
when it was good) had an article about this function, *giving the
exact values for xxx and yyy*!  (perhaps that's why I can't find any
PETs :-)

>Peter da Silva, Ferranti International Controls Corporation,
>sugar!ficc!peter.
-- 
 Clifford A. Adams  ---  "I understand only inasmuch as I become."
 ForthLisp Project Programmer   (Goal: LISP interpreter in Forth)
 caasnsr@nmtsun.nmt.edu     ...cmcl2!lanl!unm-la!unmvax!nmtsun!caasnsr