From: joe@user.com   
      
   "Mark McDougall"  wrote in message   
   news:45639840$0$1581$5a62ac22@per-qv1-newsreader-01.iinet.net.au...   
   > Frank Durda IV wrote:   
   >   
   > > There were a few sound reasons   
   > > behind this, because it was completely possible to program a Model II   
   > > to burn up its video system (complete with smoke and sometimes   
   > > flames), and a few other expensive hardware pieces were also   
   > > vulnerable to being destroyed due to not knowing what you were doing or   
   > > if you only programmed half the settings in the alloted time or   
   > > similar issues.   
   >   
   > Wow, that's incredible, and one could argue, incredibly bad design.   
   > Having said that, it's entirely possible to destroy your VGA monitor in   
   > software too.   
      
   The problem with the video was the monitor driver board.  If a sync was   
   way out of range, it could cause one of the drivers to just 'turn on solid',   
   which exceeded power disapation specs.  The problem with this was   
   that not only did the part fail, it usually shorted such that it fed 12v   
   back   
   through the driver circuit.  A lot of times it would get far enough to   
   get all the way back to the video/keyboard card.   
      
   The other problem was the disk.  It was possible to send the head to   
   the end of the screw, and there was enough torque that if you kept doing   
   it...   
      
   This was fixed in later monitor boards.  Well, not totally fixed.  They had   
   a free-run oscilator.  You had to really know what you were doing to   
   trash that one out.   
      
   > The editor's response was along the lines of it being impossible for   
   > software to cause physical harm to the computer (it was a Model I BASIC   
   > listing IIRC).   
      
   I don't know of any way to damage a Model I in software.  Although I   
   can see where some Model I programs, if run on a Model II, could do   
   it.  Hmm,  I suppose you could bang the crap out of the Tandon floppies   
   taking the carriage to the hub.  But then, that's not fair.  Almost anything   
   would wreck a Tandon floppy.  Then again, they were mostly garbage   
   when new anyway.   
      
   > And of course there's the infamous "Halt-And-Catch-Fire" instruction. ;)   
      
   If you're refering to what I think you are, the 'HCF' instruction was   
   actually   
   a 'test' instruction that Motorola put in to halt CPU execution and allow   
   external hardware to take control of the part.  STRICTLY for manufacture   
   production line testing.  Unfortunately, it seems that if executed in most   
   designs, it did just that.  Or close to it. Halt and turn on everything and   
   as   
   a result, cook.   
      
   It's amazing sometimes how much power one of those CPU chips can suck   
   up!   
      
   Mike   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)