your position is our focus
The Battery Backup Current is much higher than specified in the datasheet.
T y backup current will an d le e bac ag the GPS receiver
withouthavingtheGPSreceiverturnedo t e )intoaknownstate.
If ingthe GPSreceive backup batterycon turn
GPS ceiveronfor thefirsttime to
b knownstate(refer tion 4.2.2).
Receiver outputs valid time and position but time is off by a few seconds
T isinherentto the system. S is based theso-called GPS Time, which isauniform time
s snotkeepinstep theirregularrotation fthe
Earth. rpra icalpurposes,anotheruniform
s en defined (UTC), h differs om GPS Time by an integer number of seconds. To avoid the
u e diverging indefin from tha of the Ear rotation, a leap second is introduced in UTC
w ecessary. The choic the dates and the
nouncemen of th leap seconds are under the
r ofthe
Internationa thRotati andRefere eSystems rvice(IERS)
he batter be at undefine
noncetopu
vel if th kup volt
-clock(RTC
e is applied to
thereal-tim
re
you areus rwith nected, the
toSecringitintoa
heproblem GPS GP on
calethatdoe with o
Fo ct
cale has be whic fr
niform scal itely t th's
henever n e of
an t e
esponsibility
lEar on nc Se .Atthetimeofwriting,the
n seconds is 13 this has in e past (see
Intern onal Bureau of Weights and
ati
umber of leap but changed th
Measures) and will change in t ture. Th GPS satellites transmit t e number of leap seconds (the offset
b eandUTC,als ledUTC Offset)inthe vigationmessage cein12.5minutes.
A aGPSreceive noinformationabout enumber fleap conds
untilthisinformationis
e whichcantakeupto12.5minutes.During thistime,the receiverwill haveto
make an assumption and output a default value. u-blox has decided to output 0s in this case. Some people
wouldprefer 13s(the numberof leap seconds
at thetimebeing).Though thelatter approachseems tobean
se of cold starts right now,itisveryquestionable approach
.Asthenumberofleapsecondswillchange
soonerorlater
(theearthrotationslowsdown),theproblemmightnotoccurwhentheunitsarealreadydeployedinthefield.
W bedonetoovercomethisproble
• If one attaches a backup battery to RIS eiv the receiver run for at least 12.5
e whenpoweringitu efirsttim thereceive willstoreth UTC etinitsbatterybackupRAM
terthenextpower therec erwilluse eUTCoffs from eBBRandoutputthe
number
secondstimeimmed .
• tively, one could che hether the UTC Offse (leap secon s) has een downloaded by observing
IMEGPSmes .
this initialize the UTC offset right after a power up by sending the correct
informationwiththeUBX-AID-HUImessage.Obviously,
thisrequiresanexternalCPUtostorethesedata.
How do ANTARIS
®
4 Receivers handle changes of leap seconds
TheoutputofANTARISandANTARIS4rece b s:
5958.00,A,0000.00 S,00000. 002,E,0.00 0.37,3112 ,,A*7
235960.00,A,0000.00 S,00000. 003,E,0.00 0.37,3112 ,,A*7E
C,000000.00,A,0000.00 S,00000. 004,E,0.00 0.37,01010 ,,,A*7
000001.00,A,0000.00 S,00000. 005,E,0.00 0.37,01010 ,,,A*7
RefertoSection 4.4.6.
u-center doesn’t behave as expected
Pleaserefertotheu-center user’s guideformoreinformation.
he fu e h
etweenGPSTim ocal na on
fteracoldstart, rhas th o se
receiv dfromtheGPS satellites,
advantageas one doesn't see anytime jump in ca
sinceapotentialproblemishiddenfora longtime
hatcan m?
the ANTA
®
GPS rec er and let
minut s
(BBR).Af
pth e, r e offs
cycle, eiv th et th
ofleap iately
Alterna ck w t d b
theUBX-NAV-T sage
• If isn't feasible too, one could
iverswill easfollow
$GPRMC,23 004, 00 3, 05, 6
$GPRMC,235959.00,A,0000.00004,S,00000.00002,E,0.001,0.37,311205,,,A*75
$GPRMC, 005, 00 0, 05,
$GPRM 005, 00 1, 6 1
$GPRMC, 005, 00 4, 6 4
How to change between protocols
GPSModules-SystemIntegrationManual(SIM)(incl.ReferenceDesign) Troubleshooting
GPS.G4-MS4-05007-A1
Page 145
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