Referring to FIG. 6, a transmitter 612 of the first device 110 and a receiver 622 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 114b connected to the signal line 130, and the ODT circuit 114b may be configured as a pull-down circuit connected to the ground voltage VSSQ line. The ODT circuit 114b may include the pull-down resistor RD connected between the ground voltage VSSQ line and the signal line 130 and the pull-down switch SD disposed in correspondence to the pull-down resistor RD. The pull-down switch SD may be turned on or off according to a first ODT control signal C1b. The first ODT control signal C1b may be generated by the ODT control circuit 112. When the pull-down switch SD is turned on by the first ODT control signal C1b, the ODT circuit 114b may be ODT enabled. When the pull-down switch SD is turned off, the ODT circuit 114b may be ODT disabled.
