The correct answer is option 'B' - Port side.

Explanation:
Interface circuits are used to connect external devices or peripherals to a computer system. These circuits provide a communication path between the device and the computer, allowing data to be transferred back and forth.

There are typically two sides of an interface circuit: the port side and the device side. The port side is the side that connects to the computer system, while the device side connects to the external device or peripheral.

Data Path:
The data path refers to the physical wires or connections that carry the data between the interface and the device. It includes the necessary circuitry to transmit and receive data signals. The data path is responsible for transferring the actual data between the interface and the device.

Control Signals:
Control signals are used to coordinate and control the data transfer between the interface and the device. These signals indicate when data is ready to be transmitted, when to start and stop data transfer, and other control functions. The control signals ensure that data is transferred accurately and efficiently.

Interface and Device:
The interface circuits act as an intermediary between the computer system and the external device. The interface side connects to the computer's bus or other communication channels, allowing it to communicate with the rest of the system. The device side connects to the specific device or peripheral, providing the necessary connections and protocols for communication.

Port Side:
The port side of the interface circuit is the side that connects to the computer system. It includes the data path and control signals that facilitate data transfer between the interface and the computer. The port side is responsible for receiving data from the computer or sending data to the computer.

In summary, the port side of the interface circuit includes the data path and control signals necessary for transferring data between the interface and the computer system. It is the side that connects to the computer, while the device side connects to the external device or peripheral.