EVA-M8M - Hardware Integration Manual
UBX-14006179 - R02
Early Production Information
Design-in
Page 17 of 45
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 15).
2.6
Safe Boot Mode (SAFEBOOT_N pin)
If the SAFEBOOT_N pin is “low” at start up, the EVA-M8M series starts in Safe Boot Mode and doesn’t begin
GNSS operation. In Safe Boot Mode the EVA-M8M series 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-M8M series 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-M8M 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-M8M receivers. For
further information see the
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-M8M series starts up. This can be provided using an externally
connected test point or via a host CPUs digital I/O port.
2.7
RESET_N
The EVA-M8M modules provide 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-M8M series 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.
