EVA-M8E - Hardware Integration Manual
UBX-15028542 - R05
Contents
Page 17 of 44
Production Information
2.5.3
Improved Jamming Immunity
If strong out-band jammers are close to the GNSS antenna (e.g. a GSM antenna) GNSS performance
can be degraded or the maximum input power of the EVA-M8E module’s RF-input can be exceeded.
An additional SAW filter (F2) has to put in front of the external LNA (U1), see Appendix A. If the
external LNA can accept the maximum input power, the SAW filter between the passive antenna and
external LNA (LNA1) might not be necessary. This results in a better noise figure than an additional
SAW filter (F2) in front of the external LNA (U1).
If the EVA-M8E module is exposed to an interference environment, it is recommended to use
additional filtering. Improved interference immunity with good GNSS performance can be achieved
when using a SAW/LNA/SAW configuration between the antenna and the RF-input. The single-ended
SAW filter (F2) can be placed in front of the LNA matching network to prevent receiver blocking due
to strong interference, see Figure 16.
It should be noted that the insertion loss of SAW filter (F2) directly affects the system noise figure
and hence the system performance. Choice of a component with low insertion loss is mandatory when
a passive antenna is used with this set-up. An example schematic for an improved jamming immunity
is shown in Appendix A.3 (see Figure 16).
2.6
Safe Boot Mode (SAFEBOOT_N)
If the
SAFEBOOT_N
pin is “low” at start up, the EVA-M8E module starts in Safe Boot Mode and
doesn’t begin GNSS operation. In Safe Boot Mode the EVA-M8E module runs from an internal LC
oscillator and starts regardless of any configuration provided by the configuration pins. Thus, it can
be used to recover from situations where the SQI Flash has become corrupted.
Owing to the inaccurate frequency of the internal LC oscillator, the EVA-M8E module is unable to
communicate via USB in Safe Boot Mode. For communication by UART in Safe Boot Mode, a training
sequence (0x 55 55 at 9600 baud) can be sent by the host to the EVA-M8E in order to enable
communication. After sending the training sequence, the host has to wait for at least 2 ms before
sending messages to the EVA-M8E receiver. For further information see the
u-blox 8 / u-blox M8
Receiver Description Including Protocol Specification
[2].
Safe Boot Mode is used in production to program the SQI Flash. It is recommended to have the
possibility to pull the
SAFEBOOT_N
pin “low” when the EVA-M8E module starts up. This can be
provided using an externally connected test point or via a host CPUs digital I/O port.
2.7
System Reset (RESET_N)
The EVA-M8E module provides a
RESET_N
pin to reset the system. The
RESET_N
is an input-only
with internal pull-up resistor. It must be at low level for at least 10 ms to make sure
RESET_N
is
detected. It is used to reset the system. Leave
RESET_N
open for normal operation. The
RESET_N
complies with the
VCC_IO
level and can be actively driven high.
☞
RESET_N
should be only used in critical situations to recover the system. The Real-Time Clock
(RTC) will also be reset and thus immediately afterwards the receiver cannot perform a Hot Start.
☞
In reset state, the EVA-M8E module consumes a significant amount of current. It is therefore
recommended to use
RESET_N
only as a reset signal and not as an enable/disable.
