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190-00266-01 GPS 15H & 15L Technical Specifications Rev. D
Page 16
4.2.2 Transmitted Time
The GPS sensor outputs UTC (Coordinated Universal Time) date and time of day in the transmitted
sentences. Before the initial position fix, the on-board clock provides the date and time of day. After the
initial position fix, the date and time of day are calculated using GPS satellite information and are
synchronized with the one-pulse-per-second output.
The GPS sensor uses information obtained from the GPS satellites to add or delete UTC leap seconds and
correct the transmitted date and time of day. The transmitted date and time of day for leap second
correction follow the guidelines in National Institute of Standards and Technology Special Publication 432
(Revised 1990). This document is for sale by the Superintendent of Documents, U.S. Government Printing
Office, Washington, D.C., 20402, U.S.A.
When a positive leap second is required, one second is inserted at the beginning of the first hour (0h 0m 0s)
of the day that the positive leap is occurring. The minute containing the leap second is 61 seconds long. The
GPS sensor would have transmitted this information for the leap second added December 31, 1998 as
follows:
$GPRMC,235959,A,3851.3651,N,09447.9382,W,000.0,221.9,071103,003.3,E*69
$GPRMC,000000,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*67
$GPRMC,000000,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*67
$GPRMC,000001,A,3851.3651,N,09447.9382,W,000.0,221.9,081103,003.3,E*66
If a negative leap second should be required, one second is deleted at the end of some UTC month. The
minute containing the leap second will be only 59 seconds long. In this case, the GPS sensor will not
transmit the time of day 0h 0m 0s (the “zero” second) for the day from which the leap second is removed.
$GPRMC,235959,A,3851.3650,N,09447.9373,W,000.0,000.0,111103,003.3,E*69
$GPRMC,000001,A,3851.3650,N,09447.9373,W,000.0,000.0,121103,003.3,E*6A
$GPRMC,000002,A,3851.3650,N,09447.9373,W,000.0,000.0,121103,003.3,E*69
4.2.3 Global Positioning System Almanac Data (ALM)
Almanac sentences are not normally transmitted. Almanac transmission can be initiated by sending the
GPS sensor a $PGRMO,GPALM,1 command. Upon receipt of this command, the GPS sensor transmits
available almanac information on GPALM sentences. During the transmission of almanac sentences, other
NMEA 0183 data output is suspended temporarily.
$GPALM,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>,<14>,<15>*hh<CR><LF>
<field information> can be found in section
4.1.1.
4.2.4 Global Positioning System Fix Data (GGA)
$GPGGA,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M,<10>,M,<11>,<12>*hh<CR><LF>
<1> UTC time of position fix, hhmmss format
<2> Latitude, ddmm.mmmm format (leading zeros are transmitted)
<3> Latitude hemisphere, N or S
<4> Longitude, dddmm.mmmm format (leading zeros are transmitted)
<5> Longitude hemisphere, E or W
<6> GPS quality indication, 0 = fix not available, 1 = Non-differential GPS fix available, 2 =
differential GPS fix available, 6 = estimated (only if NMEA 0183 version 2.30 mode is enabled
in field 7 of the PGRMC1 sentence; see section
4.1.4.)
<7> Number of satellites in use, 00 to 12 (leading zeros are transmitted)
<8> Horizontal dilution of precision, 0.5 to 99.9
<9> Antenna height above/below mean sea level, -9999.9 to 99999.9 meters
<10> Geoidal height, -999.9 to 9999.9 meters
<11> Differential GPS (RTCM SC-104) data age, number of seconds since last valid RTCM
transmission (null if not an RTCM DGPS fix)
<12> Differential Reference Station ID, 0000 to 1023 (leading zeros are transmitted, null if not an
RTCM DGPS fix)