An adoption of NMEA0183 (National Marine electronics Association) at RS-232 voltage levels is used for the data link between level 1 and level 2. The standard was chosen on the following basis: It has a low power consumption, the bandwidth requirements are low, it is human readable, and the signal can be tapped for easy debugging. Level 1 will once per second transmit a request for rudder and commands to the Level 2, in the form of a NMEA message.

There are three kind of NMEA-like messages involved for different communications: - Level 2 - Level 1 communication; - Level 1 - Operator bilateral communication.

Level 2 sends messages to Level 1 containing the desired rudder angle and thruster intensity. These come as a result of high-level control (PIDs) implemented in DUNE. The format of this message is:
;#; MSG = BBB01 , RUD , THR , PWR_SETT , FALLB_MODE ;#; Where:
- BBB01 is the msg ID;
- RUD is the rudder angle [-450,450];
- THR is the thruster intensity [-100,100];
- PWR_SETT are the power settings: 6-bits string where 1 disables and 0 enables;
- FALLB_MODE selects the fallback mode: 0 for rudder 0, 1 for circle, 2 for autopilot.

The operator can comminicate to Level 1 through Neptus (Java Plugin), sending messages that respect this format:
;#; MSG = RCC01 , RUD , THR , Kp , Ki , PWR_SETT , FALLB_MODE , MANUAL_CTRL ;#; Where:
- RCC01 is the msg ID;
- RUD is the rudder angle [-450,450];
- THR is the thruster intensity [-100,100];
- Kp and Ki set the gains for the Level 1 Fallback Autopilot;
- PWR_SETT are the power settings: 6-bits string where 1 disables and 0 enables;
- FALLB_MODE selects the fallback mode: 0 for rudder 0, 1 for circle, 2 for autopilot;
- MANUAL_CTRL is a boolean: 1 for taking control (manual), 0 for giving control (autopilot).

Level 1 can send messages to the Operator showing the status of the system. These massage have the following format:
;#; MSG = CR601 , LEAK , PWR_SETT , LOAD, PANEL1_2 , BATT , COG , SOG , N_SAT , LAT , LONG , Kp , Ki , e , int_e , RUD , THRUST , L1_STATE , FALLB_MODE ;#; Where:
- CR601 is the msg ID;
- LEAK indicates a leak is happening: 1 for TRUE, 0 for FALSE;
- PWR_SETT indicates the power settings: 6-bits string where 1 means disabled and 0 enabled;
- LOAD is the load power (W);
- PANEL1_2 is the panel 1 and panel 2 power (W);
- BATT is the voltage battery (V);
- COG is the course over ground (°);
- SOG is the speed over ground (kn);
- N_SAT is the satellites number used by the GPS;
- LAT is the latitude;
- LONG is the longitude;
- Kp and Ki are the gains used by the PI fallback autopilot controller;
- e is the error;
- int_e is the integrated error;
- RUD is the rudder computed by the PI fallback autopilot controller;
- THR is the thruster applied to the servo;
- L1_STATE shows the operating state of L1: 1 = normal, 2=fallback, 3=manual;
- FALLB_MODE selects the fallback mode: 0 for rudder 0, 1 for circle, 2 for autopilot.