code: def instruction_NEG_register(self, opcode, register):
          
          x = register.value
          r = x * -1 # same as: r = ~x + 1
          register.set(r)
  #        log.debug("$%04x NEG %s $%02x to $%02x" % (
  #            self.program_counter, register.name, x, r,
  #        ))
          self.clear_NZVC()
          self.update_NZVC_8(0, x, r)
docs: Replaces the register with its twos complement. The C (carry) bit
          represents a borrow and is set to the inverse of the resulting binary
          carry. Note that 80 16 is replaced by itself and only in this case is
          the V (overflow) bit set. The value 00 16 is also replaced by itself,
          and only in this case is the C (carry) bit cleared.
  
          source code forms: NEG Q; NEGA; NEG B
  
          CC bits "HNZVC": uaaaa