code: def instruction_DEC_register(self, opcode, register):
          
          a = register.value
          r = self.DEC(a)
  #        log.debug("$%x DEC %s value $%x -1 = $%x" % (
  #            self.program_counter,
  #            register.name, a, r
  #        ))
          register.set(r)
docs: Decrement accumulator