Rtc Using A Crystal; Rtc Using An External Clock; Time Aiding - Ublox ZOE-M8B Series System Integration Manual

ZOE-M8B - System Integration Manual
The time information can either be generated by connecting an external RTC crystal to the SiP, by
connecting an external 32.768 kHz signal to the RTC input, or by time aiding of the GNSS receiver at
every startup.

2.4.1 RTC using a crystal

The easiest way to provide time information to the receiver is to connect an RTC crystal to the
corresponding pins of the RTC oscillator, RTC_I and RTC_O. There is no need to add load capacitors
to the crystal for frequency tuning, because they are already integrated in the chip. Using an RTC
crystal will provide the lowest current consumption to V_BCKP in case of a power failure. On the other
hand, it will increase the BOM costs and requires space for the RTC crystal.
Figure 12: RTC crystal

2.4.2 RTC using an external clock

Some applications can provide a suitable 32.768 kHz external reference to drive the SiP RTC. The
external reference can simply be connected to the RTC_I pin. Make sure that the 32.768 kHz reference
signal is always turned on and the voltage at the RTC_I pin does not exceed 350 mVpp. Adjusting of
the voltage level (typ. 200 mVpp) can be achieved with a resistive voltage divider followed by a DC
blocking capacitor in the range of 1 nF to 10 nF. Also make sure the frequency versus temperature
behavior of the external clock is within the recommended crystal specification shown in section A.1.

2.4.3 Time aiding

Time can also be sent by UBX message at every startup of the ZOE-M8B GNSS SiP to enable warm
starts, AssistNow Autonomous and AssistNow Offline. This can be done when no RTC is maintained.
To enable hot starts correctly, the time information must be known accurately and thus the
TimeMark feature has to be used.
u-blox 8 / u-blox M8 Receiver Description
For more information about time aiding or timemark see the
Including Protocol Specification
[3].
☞
For information of this use case, it is mandatory to contact u-blox support team.
2.5 RF input
The ZOE-M8B GNSS SiP RF input is already matched to 50 Ω and has an internal DC block. The ZOE-
M8B SiP is optimized to work with passive antenna.
The ZOE-M8B GNSS SiP can receive and track multiple GNSS systems (e.g. GPS, Galileo, GLONASS,
BeiDou and QZSS signals). Because of the dual-frequency RF front-end architecture, two GNSS
signals (GPS L1C/A, GLONASS L1OF, Galileo E1B/C and BeiDou B1) can be received and processed
concurrently. In continuous mode, this concurrent operation is extended to three GNSS when GPS and
Galileo are used in addition to GLONASS or BeiDou.
UBX-17045131 - R04 Contents Page 18 of 42
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