Source : Free On-Line Dictionary of Computing

Halt and Catch Fire
     
         (HCF) Any of several undocumented and
        semi-mythical {machine instructions} with destructive
        side-effects, supposedly included for test purposes on several
        well-known architectures going as far back as the {IBM 360}.
        The {Motorola} {6800} {microprocessor} was the first for which
        an HCF {opcode} became widely known.  This instruction caused
        the processor to {toggle} a subset of the {bus} lines as
        rapidly as it could; in some configurations this could
        actually cause lines to burn up.
     
        [Confirm?]
     
        (1995-12-14)