A command storing control circuit stores in storing units a plurality of commands supplied the latest of the supplied commands so as to execute the memory operation. A command reading control circuit reads the commands stored in a command storing area during a test mode. If incorrect data are written into a semiconductor memory, causing the system mounting the semiconductor memory to become inoperable, the cause of the trouble can be efficiently determined by utilizing the commands stored in the command storing area. As a result, the efficiency of development of the system can be improved, for example, and the cost of developing the system can be reduced. Moreover, the quality of the system can be also improved.
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