An intelligent cable is disclosed. The cable provides a connector and a metal core. The connector is pluggably coupled with an external apparatus and enclosing a circuit unit electrically connected to an external apparatus. The metal core is electrically connected to the circuit unit in the connector. The circuit unit includes a transmitter and a receiver. The transmitter receives input signals from the external apparatus and outputs a transmitted signal to the metal core. The receiver receives the transmitted signal from the metal core and provides output signals to the external apparatus. A feature of the cable is that the transmitter modulates the input signals and the receiver de-modulates the transmitted signal both by the PAM configuration.