It is possible to communicate with more than 1 serial line from the 2560 board to other devices, so why not communicate to a second device for sending and receiving commands for supervisory control and data acquisition of the board (scada)? A serial RS232 line could make serial communication, a serial to USB (radio) connection or for example a Bluetooth connection. The standard sketch, supports functions for communication. Via the extra serial line the board is able to receive and send commands from another device. The "other" device is always the master and the Arduino board acts as a slave capable of executing all commands to control or influence the main loop of the finite state machine. Some examples of probable HMI's are a terminal program (simple) or a Visual Studio program. The only thing to do on the HMI master, is sending commands and process the received data from the board. No extra programming is needed on the board! It is only necessary to set a variable in the sketch (boolean UseHMISerial=true; or false when you decide not using the extra serial line). You also have to program the setup of the serial line (this is not necessary when TX1/RX1 is used; this is standard).
Above the APC220 RF set. Ideal for a serial connection between the board and a PC. Some shields for the MEGA2560 are standard equipped for this RF set. The PC side communicates via the USB connector block. The set is able to communicate over a sight distance of 1000m. I've tested this set over a distance of 500m and still worked with the AFSM.
 Fetching data with a certain frequency is called polling.