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Diffstat (limited to 'www/NMEA.adoc')
| -rw-r--r-- | www/NMEA.adoc | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/www/NMEA.adoc b/www/NMEA.adoc index eb10cdd4..f3594fd2 100644 --- a/www/NMEA.adoc +++ b/www/NMEA.adoc @@ -210,12 +210,13 @@ second and the following subframe broadcast. GPS date and time are subject to a rollover problem in the 10-bit week number counter, which will re-zero every 1024 weeks (roughly every 19.6 -years). The last rollover (and the first since GPS went live in 1980) -was in Aug-1999; the next will fall in Apr-2019. The new "CNAV" data +years). The first rollover since GPS went live in 1980 was in Aug-1999, +followed by Apr-2019, the next will be in Nov-2038 (the 32-bit and POSIX +issues will probably be more important by then). The new "CNAV" data format extends the week number to 13 bits, with the first rollover occurring in Jan-2137, but this is only used with some newly added GPS signals, and is unlikely to be usable in most consumer-grade receivers -prior to the 2019 rollover. +currently. For accurate time reporting, therefore, a GPS requires a supplemental time references sufficient to identify the current rollover period, @@ -1241,6 +1242,17 @@ Field Number: Example: $GNGSA,A,3,80,71,73,79,69,,,,,,,,1.83,1.09,1.47*17 +Note: NMEA 4.1+ systems (in particular u-blox 9) emit an extra field +just before the checksum. + +----------------------------------------------- +1 = GPS L1C/A, L2CL, L2CM +2 = GLONASS L1 OF, L2 OF +3 = Galileo E1C, E1B, E5 bl, E5 bQ +4 = BeiDou B1I D1, B1I D2, B2I D1, B2I D12 +----------------------------------------------- + + === GSV - Satellites in view === This is one of the sentences commonly emitted by GPS units. |