Referring to FIG. 2, a transmitter 212 of the first device 110 and a receiver 222 of the second device 120 may be connected to each other through the signal line 130. The first device 110 may include the ODT circuit 114a connected to the signal line 130, and the ODT circuit 114a may be configured as a pull-up circuit connected to a power voltage (VDDQ) line. The ODT circuit 114a may include a pull-up resistor RU connected between the power voltage VDDQ line and the signal line 130 and a pull-up switch SU arranged in correspondence to the pull-up resistor RU. The pull-up switch SU may be turned on or off according to a first ODT control signal C1a. The first ODT control signal C1a may be generated by the ODT control circuit 112. When the pull-up switch SU is turned on by the first ODT control signal C1a, the ODT circuit 114a may be ODT enabled. When the pull-up switch SU is turned off, the ODT circuit 114a may be ODT disabled.
