HCF

HCF /H-C-F/ n.  Mnemonic for `Halt and Catch Fire', 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 MC6800 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.