RGPSM202 Semtech, RGPSM202 Datasheet - Page 20

• Manufacturer Part Number: RGPSM202
• Description: MODULE SLIM GPS RECEIVER LP
• Manufacturer: Semtech

Specifications of RGPSM202

• Frequency: 1.575GHz
• Sensitivity: -143dBm
• Modulation Or Protocol: GPS
• Applications: Automotive, Laptop, PDA
• Current - Receiving: 25mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 3 V ~ 3.65 V
• Package / Case: Module
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Operating Temperature: -
• Memory Size: -
• Data Rate - Maximum: -

5.4.10.1 Set the RTC time
The purpose of GPS time is to allow use of the almanac data and position to determine which satellites are in view and
to allow rough ranging to the satellites. XE1610-PVT products load GPS time every start-up. If the local RTC, from
which this GPS time is loaded, is not valid it is possible to provide the GPS time from another source. The accuracy of
this external source should be better than 30 minutes.
The time/date information in the GPS system is coded using a standard GPS time format that is a week number and the
time of the week. The week number of the GPS time is the number of weeks from Sunday, January 6 1980. However,
due to the GPS data message format, the week number is a modulo-1024 number (10-bit number). The last rollover
occurred on August 22, 1999. The next rollover will happen on April 7, 2019. The GPS time of the week is the number
of milliseconds since the beginning of the current GPS week, the GPS week starting on Sundays at 0 hour, 0 minute, 0
millisecond.
When the GPS engine is running the TR sentence to use is:
$PXEMSTR,SSIT,WeekNb,TimeOfWeek,Accu*hh
where:
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Important notes:
- if the Accu parameter is set to 1, the hardware RTC will be updated when receiving this command
- if the Accu parameter is set to -1, the hardware RTC will NOT be updated when receiving the sentence
- if the Accu parameter is set to another negative value, the hardware RTC will be updated when receiving the
sentence.
Also, it is strongly advised to avoid setting the Accu parameter to 1 if one is not sure about the accuracy, as this may
lead to improper behavior.
5.4.10.2 Set the initial position
The purpose of the rough initial position is to allow use of the almanac data and GPS time to determine which satellites
are in view. This is achieved by sending a proprietary TR command which format is:
$PXEMSTR,SSIP,L.LLL,O.OOO,Alt,Accu*hh
where:
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For example, to set the position to New Delhi in India (coordinates being lat: 0.499, lon: 1.347), the full sentence should
be:
$PXEMSTR,SSIP,0.499,1.347,200,-1*hh
The initial position can only be set when the GPS engine is running and before the system does position fix. Note that
an initial position error of 1,000 km will result in an almanac based satellite search set which has rotated out of view by
approximately 10%. Beyond this, the specified performance will degrade. Initial position errors greater than 3,000 km
will result in a constellation which is almost out of view. So, the recommendation is to set the initial position only if its
accuracy is better than 1,200 km.
© Semtech 2005
WeekNb is the week number (see above)
TimeOfWeek is the time of the week information, in milliseconds (see above)
Accu (integer value) reflects the accuracy of the time information provided to the system. Use 1 only if the time of
the week and the week number are valid (accuracy better than 30 minutes), otherwise -1
L.LLL is the latitude expressed in radian
O.OOO is the longitude expressed in radian
Alt is the altitude expressed in meter. Note that if you are not sure about the altitude, a default value of 200 gives
acceptable results in most cases.
Accu reflects the accuracy of the initial position. Use -1
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SlimGPS™ Receiver
RGPSM202
www.semtech.com