Port is used to initialize, monitor, and control the receiver.
For more details, please refer to the NMEA-0183 Specification available from the National Marine Electronics Association . Reserved characters are used to indicate the beginning and the end of records in the data stream, and to delimit data fields within a sentence. Table 2 lists the reserved characters and defines their usage. Table 1 illustrates the general Magnavox proprietary NMEA sentence format. The next field after the block label is the sentence type, consisting of three decimal digits.