When the ODT control circuit 112 determines that the ODT state of the first device 110 and the ODT state of the second device 120 are different from each other, the first device 110 may provide an asymmetric termination parameter code to the second device 120. The asymmetric termination parameter code may be transmitted to the second device 120 through the signal line 130. The ODT control circuit 112 may generate a first ODT control signal C1 based on the ODT state of the first device 110 and the ODT state of the second device 120 being different from each other, and provide the first ODT control signal C1 to the ODT circuit 114. The ODT circuit 114 may perform an ODT enable or disable operation according to the first ODT control signal C1.

The second device 120 may include a mode register set 121 (hereinafter referred to as ‘MRS’), a control circuit 122 and an ODT circuit 124. The MRS 121 may be programmed to set operating parameters, options, various functions, characteristics, and modes of the second device 120. The MRS 121 may include a register that stores parameter codes with respect to various operation and control parameters used to set operating conditions of the second device 120. The MRS 121 may store a parameter code including appropriate bit values provided to command/address signal lines when an MRS command is issued from the first device 110. The MRS 121 may store the asymmetric termination parameter code transmitted from the first device 110 through the command/address signal lines. The asymmetric termination parameter code will be described later with reference to FIG. 14.