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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.