Final answer:
In UART operation, the Idle state is the one waiting for the 'ready to transmit' flag. It is not active in sending or receiving but is prepared to start transmitting once the data is ready and the flag is set.
Step-by-step explanation:
Illustration 3 is likely referring to a state diagram or flowchart related to the operation of a Universal Asynchronous Receiver/Transmitter (UART), which is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. The specific state that waits for a UART flag indicating it is ready to transmit a character is typically the Idle state. In this state, the UART is not actively sending or receiving data, but is ready and waiting for the transmit buffer to be filled with data and for the transmit ready flag (often called TX ready or TX complete) to be set, indicating that the UART can start the data transmission process.
In contrast, the Transmitting state is when the UART is actively sending data, the Receiving state is when it is receiving data, and the Processing state may refer to internal operations such as error checking or preparing data for transmission or further processing after reception.