A slave device includes a first connector, a second connector, a switch, and a communication circuit. The switch is alternatively connectable to the first connector or the second connector according to a connection way via which the slave device is connected to a master device and another slave device. The communication circuit is connected to the first connector and the switch. The communication circuit is configured to transmit and receive a first communication signal to and from the first connector, and is configured to transmit and receive a second communication signal to and from the switch.