Garmin GPS 18 Technical Specifications

Also see for GPS 18 5Hz: Reference guide Features Setup guide

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Garmin GPS 18 Technical Specifications Manual pdf 18 page image

GPS 18 Technical Specifications (190-00307-00) Rev. DPage 124 GPS 18 PC, GPS 18 LVC, & GPS 18-5Hz SOFTWARE INTERFACEThe interface protocol design of the GPS 18 PC, LVC, and GPS 18-5Hz products is based on the NationalMarine Electronics Association’s NMEA 0183 ASCII interface specification. This standard is fully definedin NMEA 0183, Version 2.30. Copies may be obtained from NMEA, www.nmea.org.In addition to the standard NMEA 0183 sentences, the GPS 18 PC, LVC, and GPS 18-5Hz may also beconfigured to transmit information over their serial interface using NMEA 0183 compliant Garminproprietary sentences. These proprietary sentences begin with the characters, “$PGRM”, instead of thecharacters “$G” that are typical of the standard NMEA 0183 sentences. The characters “$P” indicate thatthe sentence is a proprietary implementation and the characters and “GRM” indicate that it is Garmin’sproprietary sentence. The letter (or letters) that follow the characters “$PGRM” uniquely identifies thatparticular Garmin proprietary sentence.It is also possible to configure the GPS 18 PC, LVC, and GPS 18-5Hz to transmit binary phase datainformation over their serial interface. See Appendix B: Binary Phase Output Format for details.The GPS 18 USB does not transmit NMEA sentences: It transmits using the Garmin USB interface. TheGarmin USB interface is discussed in the Garmin Device Interface Specification located on the GarminWeb site at: http://www.garmin.com/support/commProtocol.html. You can configure the GPS 18 USB totransmit binary phase data information over the USB interface. Refer to Appendix B: Binary Phase OutputFormat.The following sections describe the NMEA 0183 data format of each sentence transmitted and received bythe GPS 18 PC, LVC, and GPS 18-5Hz products.4.1 RECEIVED NMEA 0183 SENTENCESThe following paragraphs define the sentences that can be received on the GPS sensors’ port. Null fields inthe configuration sentence indicate no change in the particular configuration parameter. All sentencesreceived by the GPS sensor must be terminated with , the ASCII characters for carriage return(0D hexadecimal) and line feed (0A hexadecimal). The checksum *hh is used for parity checking data andis not required, but is recommended for use in environments containing high electromagnetic noise. It isgenerally not required in normal PC environments. When used, the parity bytes (hh) are the ASCIIrepresentation of the exclusive-or (XOR) sum of all the characters between the “$” and “*” characters, non-inclusive. The hex representation must be a capital letter, such as 3D instead of 3d. Sentences may betruncated by after any data field and valid fields up to that point will be acted on by the sensor.4.1.1 Almanac Information (ALM)The $GPALM sentence can be used to initialize the GPS sensor’s stored almanac information in theunlikely event of non-volatile memory loss or after storing longer than six months without tracking GPSsatellites.$GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15>*hh<1> Total number of ALM sentences to be transmitted by the GPS sensor during almanac download.This field can be null or any number when sending almanac to the GPS sensor.<2> Number of current ALM sentence. This field can be null or any number when sending almanacto the GPS sensor.<3> Satellite PRN number, 01 to 32<4> GPS week number<5> SV health, bits 17–24 of each almanac page<6> Eccentricity<7> Almanac reference time<8> Inclination angle<9> Rate of right ascension<10> Root of semi major axis<11> Omega, argument of perigee<12> Longitude of ascension node<13> Mean anomaly<14> af0 clock parameter<15> af1 clock parameter