Using GE864-GPS (GPS controlled by external host) Help

8 thoughts on “Using GE864-GPS (GPS controlled by external host) Help

  1. Hi guys,
    My problems is the lack of information in "GE864-GPS Hardware User Guide". In the section about GPS_WAKEUP and GPS_ON_OFF signals they say :

    The GPS starts after asserting a rising edge pulse on GPS_ON_OFF input and when high 
    level persists for at least three cycles of RTC clock. Before asserting another pulse to 
    GPS_ON_OFF input, the host controller must put it at low state and hold it low for at least 
    three cycles of the RTC clock

     I was reading:

    • Telit_GE/GC864-QUAD_V2_and_GE864-GPS_Hardware_User Guide_r12
    • Telit_AT_Commands_Reference_Guide_r17
    • Telit_Using_SiRF_STAR_IV_with_an_external_Host_Application_Note_r0

    The GE864-GPS has included the RTC, but I can not find it anywhere about the RTC clock. I know the most RTC used a crystal of 32.768Khz and some product of Telit too. Of course I’m waiting the answer of my distribuitor but I don’t lose anything asking here.

    Does anyone know anything about this?


  2. Thank you, I was reading all available documents for GE864-GPS and nothing about it.

    For example, in the document "Telit_Jupiter_JF2_Hardware_User_Guide_r4" at page 12

    you can see how specify this information. But for GE864-GPS I cannot find anything.


  3. We use GPS for timing. What is the relationship between the 1PPS signal and the time in the RMC message for the JN3?


    What parts are recommended for new designs? 

  4. Hello Dave,


    For SirfStar IV based products (JF2-JN3), note that the
    1pps pulse has not been verified or characterized for all operational
    conditions. But, the 1pps pulse is a 200ms positive going pulse, typical ±200ns
    with 450ns offset referenced to UTC one-second boundaries under 3D navigation


    Note:The GPS receiver will only provide 1PPS when a 3D fix has
    been obtained using 5 
    SVs. When the fix degrades below a 3D solution, the 1PPS will be
    blanked. Once the fix 
    quality improves back to a 3D fix the 1PPS will again be output.



    However  the JN3 uses a SiRF Star IV IC GPS receiver.
    This platform, while it does provides 1PPS signal, isn’t a timing receiver. We
    have a product that is a timing receiver. It’s the SL869, which is based on the
    ST-Micro GNSS Teseo II receiver IC. It uses the same footprint as the JN3 and
    is pin to pin compatible. 

    1. Thanks.


      What is the relationship between the 1PPS signal and the time in the RMC message?

      1.  Hi,
        The 1PPS signal for both solutions align themselves to UTC one-second boundaries.
        At every UTC 1-second boundary, the PPS should fire and measurements and calculations are made. 
        After these measurements, the NMEA messages are created that have information that are valid for that UTC 1-second boundary. (note that there will be latency when the NMEA messages are actually outputted – about 300ms after the 1PPS occurs and NMEA is outputted for JN3) .                                        
         We recommend to use the $GPRMC message since it is the first message outputted by both receivers.