Abstract: A method of entering memory module mounted on a memory system or a plurality of memories mounted on the memory module into a test mode, and a first register and a second register for performing the method are introduced. Each of the memory manufacturers provides a different MRS code for entering the memory into the test mode and a different method of entering the memory into the test mode from one another. As a result, the number of the test MRS is stored in the first register for controlling the memory, and the test MRS codes are programmed into the second register. Additionally, each of the bits stored in the first register used for determining the number of the test MRS corresponds to each of the second registers that store a corresponding test MRS code, respectively.