EVA-M8E - Hardware Integration Manual
UBX-15028542 - R05
Contents
Page 15 of 44
Production Information
layout with a robust grounding concept is essential in order to protect against EMI. More information
can be found in subsection 2.13.5.3.
2.4
Real-Time Clock (RTC)
The use of the RTC is optional to maintain time in the event of power failure at
VCC_IO
. The RTC is
required for hot start, warm start, AssistNow Autonomous, AssistNow Offline and in some Power
Save Mode operations.
The time information can either be generated by connecting an external RTC crystal to the EVA-M8E
module, 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 4: RTC crystal
2.4.2
RTC using an external clock
Some applications can provide a suitable 32.768 kHz external reference to drive the EVA-M8E 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 B.1.
2.4.3
Time aiding
Time can also be sent by UBX message at every startup of the EVA-M8E module. This can be done 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.
For more information about time aiding or timemark see the u-blox 8 / u-blox M8 Receiver Description
Including Protocol Specification [2].
☞
For information of this use case, it is mandatory to contact u-blox support team.
☞
For Power Save Mode operations where the RTC is needed, the time aiding cannot be used. This is
because the host does not have any information about when the EVA-M8E module turns from OFF
status to ON status during ON/OFF operation of Power Save Mode.
