ZOE-M8B - System Integration Manual
UBX-17045131 - R04
Contents
Page 17 of 42
Production Information
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For more information about supported SQI Flash devices see section A.3.
2.3
I/O Pins
All I/O pins make use of internal pull-ups to
VCC
. Thus, there is no need to connect unused pins to
VCC
.
2.3.1
External interrupt
EXTINT
is an external interrupt pin with fixed input voltage thresholds with respect to
VCC
(see the
ZOE-M8B Data Sheet [1] for more information). It can be used for wake-up functions in Power Save
Mode on all u-blox M8 modules and for aiding, leave open if unused. By default, the external interrupt
is disabled. If
EXTINT
is not used for an external interrupt function, the pin can be used as a generic
PIO (PIO13).
For further information, see the
u-blox 8 / u-blox M8 Receiver Description Including Protocol
Specification [3].
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If the
EXTINT
is configured for on/off switching of the ZOE-M8B GNSS SiP, the internal pull-up
becomes disabled. Thus make sure the
EXTINT
input is always driven within the defined voltage
level by the host.
2.3.2
External LNA enable
LNA_EN
pin can be used to turn on and off an external LNA. The external LNA can be automatically
duty cycled in Super-E mode or turned off in software backup mode.
2.3.3
Electromagnetic interference and I/O lines
Any I/O signal line (length > ~3 mm) can act as an antenna and may pick up arbitrary RF signals
transferring them as noise into the GNSS receiver. This specifically applies to unshielded lines, lines
where the corresponding GND layer is remote or missing entirely, and lines close to the edges of the
printed circuit board. If for example, a cellular signal radiates into an unshielded high-impedance line,
it is possible to generate noise in the order of volts and not only distort receiver operation but also
damage it permanently.
On the other hand, noise generated at the I/O pins will emit from unshielded I/O lines. Receiver
performance may be degraded when this noise is coupled into the GNSS antenna (see Figure 22).
In case of improper shielding, it is recommended to use resistors or ferrite beads (see Appendix A.6)
on the I/O lines in series. These components should be chosen with care because they will affect also
the signal rise times. Alternatively, feed-thru capacitors with good GND connection close to the GNSS
receiver can be used (see Appendix A.7).
EMI protection measures are particularly useful when RF emitting devices are placed next to the
GNSS receiver and/or to minimize the risk of EMI degradation due to self-jamming. An adequate
layout with a robust grounding concept is essential in order to protect against EMI. More information
can be found in section 2.14.6.3.
2.4
Real-Time Clock (RTC)
The use of the RTC is optional to maintain time in the event of power failure at
VCC
. It requires
V_BCKP
to be supplied in case of power failure at
VCC
. The RTC is required for hot start, warm start,
AssistNow Autonomous, AssistNow Offline and in some Power Save Mode operations.
