Garmin GPS 15L Technical Specifications

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Garmin GPS 15L Technical Specifications Manual pdf 34 page image

190-00266-01 GPS 15H & 15L Technical Specifications Rev. DPage 30Ephemeris Download ProcedureThe following is the sequence of events that occurs when downloading ephemeris data.Send a packet containing the command that requests ephemeris data (IOP_DOWN_LOAD_EPH). Thepacket should look like this:TX Packet: Ephemeris Data RequestByte Description Name HEX ValueDelimiter DLE 0x10Command Data ID IOP_CMND_DATA 0x0ANumber of bytes in data SIZE 0x02Request to D/L ephemeris IOP_DOWN_LOAD_EPH 0x5DPad to 2 bytes DATA 0x00Checksum calculation CHKSUM 0x97*Delimiter DLE 0x10End ETX 0x03* From now on, checksum calculation will not be shown for every packet exampleThe unit returns an acknowledgement packet that looks like this:RX Packet: AcknowledgementByte Description Name HEX ValueDelimiter DLE 0x10Acknowledgement ID IOP_ACK_BYTE 0x06Number of bytes in data SIZE 0x02Request to D/L ephemeris IOP_CMND_DATA 0x0APad DATA 0x00Checksum calculation CHKSUM ----Delimiter DLE 0x10End of packet ETX 0x03Then, the unit immediately sends a packet communicating how many data packets to expect for theephemeris download (a maximum of twelve):RX Packet: Number of Data Packets to ExpectByte Description Name HEX ValueDelimiter DLE 0x10Record ID IOP_RECORDS 0x1BNumber of bytes in data SIZE 0x02Number of records NUM_SV 0x0CPad DATA 0x00Checksum calculation CHKSUM ----Delimiter DLE 0x10End of packet ETX 0x03This packet requires acknowledgement, as shown below (note that the data field contains theIOP_RECORDS ID to indicate the acknowledgement of the IOP_RECORDS packet):TX Packet: AcknowledgementByte Description Name HEX ValueDelimiter DLE 0x10Record ID IOP_ACK_BYTE 0x06Number of bytes in data SIZE 0x02Pad DATA 0x00ID of packet being ACK’d IOP_RECORDS 0x1BChecksum calculation CHKSUM ----Delimiter DLE 0x10End of packet ETX 0x03