Garmin GPS 15L Technical Specifications

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Garmin GPS 15L Technical Specifications Manual pdf 15 page image

190-00266-01 GPS 15H & 15L Technical Specifications Rev. DPage 114 GPS 15H & 15L SOFTWARE INTERFACEThe GPS 15H & 15L interface protocol design on COM 1 is based on the National Marine ElectronicsAssociation’s NMEA 0183 ASCII interface specification. The COM 2 port can receive differential GPS(DGPS) correction data using the Radio Technical Commission for Maritime Services’ RTCM SC-104standard. These standards are fully defined in NMEA 0183, Version 3.0 (copies may be obtained fromNMEA, www.nmea.org) and RTCM Recommended Standards For Differential Navstar GPS Service,Version 2.2, RTCM Special Committee No.104 (copies may be obtained from RTCM, www.rtcm.org).The GPS 15H & 15L interface protocol, in addition to transmitting navigation information as defined byNMEA 0183, transmits additional information using the convention of Garmin proprietary sentences.These proprietary sentences begin with the characters, “$PGRM”, instead of the characters “$G” that aretypical of the standard NMEA 0183 sentences. The characters “$P” indicate that the sentence is aproprietary implementation and the characters and the characters “GRM” indicate that it is Garmin’sproprietary sentence. The letter (or letters) that follow the characters “$PGRM” uniquely identifies thatparticular Garmin proprietary sentence.Binary phase data information can alternatively be output on the COM 1 port; see Appendix B: BinaryPhase Output Format for details.The following sections describe the NMEA 0183 data format of each sentence transmitted and received bythe GPS 15H & 15L.4.1 RECEIVED NMEA 0183 SENTENCESThe following paragraphs define the sentences that can be received on the GPS sensor’s 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), respectively. The checksum *hh is used for paritychecking data and 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 upper and lower nibbles of the exclusive-or (XOR) sum of all the characters betweenthe “$” and “*” characters, non-inclusive. The hex representation must be a capital letter, such as 3Dinstead of 3d. Sentences may be truncated by after any data field and valid fields up to thatpoint will be acted on by the sensor.4.1.1 Almanac Information (ALM)The $GPALM sentence can be used to initialize the GPS sensor’s stored almanac information in theunlikely event of non-volatile memory loss, or after storage of greater than six months without trackingGPS satellites.$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 almanacdownload. 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 sendingalmanac to 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