The checksum is the XOR (exclusive OR) of all bytes between $ (excluded) and * (excluded).
Despite being replaced in high-end commercial maritime applications by the faster, binary-based NMEA 2000 standard, NMEA 0183 remains the dominant protocol for hobbyists, developers, and legacy commercial fleets. Its simplicity—requiring only a serial UART connection—ensures that NMEA sentences will remain a staple of interfacing electronics for years to come. nmea 0183 sentences
For example, a sentence starting with $PGRM indicates a proprietary sentence from Garmin. The checksum is the XOR (exclusive OR) of
$SDDPT,12.5,0.0,5.0*7D
A typical NMEA 0183 sentence consists of: binary-based NMEA 2000 standard