EVK-M8F-0-01 - User Guide
UBX-15016541 - R01
Early Production Information
Troubleshooting
Page 17 of 21
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Troubleshooting
My application (e.g. u-center) does not receive anything
Check whether the blue LED on the evaluation unit is blinking. Also make sure that the USB cable is properly
connected to the evaluation unit and the PC. By default, the evaluation unit outputs NMEA protocol on Serial
Port 1 at 9600 Bd, or on the USB.
My application (e.g. u-center) does not receive all messages
When using UART, make sure the baud rate is sufficient. If the baud rate is insufficient, the GNSS receiver will
skip excessive messages. Some
serial port cards/adapters (i.e. USB to RS232 converter) frequently generate
errors. If a communication error occurs while u-center receives a message, the message will be discarded.
My application (e.g. u-center) loses the connection to the GNSS receiver
u-blox M8 positioning technology and u-center have an autobauding feature. If frequent communication errors
occur (e.g. due to problems with the serial port), the connection may be lost. This happens because u-center
and the GNSS receiver both autonomously try to adjust the baud rate. Do not enable the u-center autobauding
feature if the GNSS receiver has the autobauding flag enabled.
The COM port does not send any messages
Be sure that the slide switch at the front panel is set to I2C and not SPI. In SPI Mode the RS232 pins on the DB9
connector are switched off and the RxD and TxD output at the front panel are used for SPI (MISO, MOSI).
NOTE: After changing the slide switch, always reset the EVK, otherwise the change will not take place.
Some COM ports are not shown in the port list of my application (e.g. u-center)
Only the COM ports that are available on your computer will show up in the COM port drop down list. If a COM
Port is gray, another application running on this computer is using it.
The position is off by a few dozen meters
u-blox M8 GNSS technology starts up with the WGS84 standard GNSS datum. If your application expects a
different datum, you’ll most likely find the positions to be off by a few dozen meters. Don’t forget to check the
calibration of u-center map files.
The position is off by hundreds of meters
Position drift may also occur when almanac navigation is enabled. The satellite orbit information retrieved from
an almanac is much less accurate than the information retrieved from the ephemeris. With an almanac only
solution, the position will only have an accuracy of a few kilometers but it may start up faster or still navigate in
areas with obscured visibility when the ephemeris from one or several satellites have not yet been received. The
almanac information is NOT used for calculating a position, if valid ephemeris information is present, regardless
of the setting of this flag.
In NMEA protocol, position solutions with high deviation (e.g. due to enabling almanac navigation) can be
filtered with the
Position Accuracy Mask. UBX protocol does not directly support this since it provides a position
accuracy estimation, which allows the user to filter the position according to his requirements. However, the
‘Position within Limits’ flag of the UBX-NAV-STATUS message indicates whether the configured thresholds (i.e. P
Accuracy Mask and PDOP) are exceeded.
The EVK-M8F does not meet the TTFF specification
Make sure the antenna has a good sky view. An obstructed view leads to prolonged startup times. In a well-
designed system, the average of the C/No ratio of high elevation satellites should be in the range of 40 dBHz to
about 50 dBHz. With a standard off-the-shelf active antenna, 47 dBHz should easily be achieved. Low C/No
values lead to a prolonged startup time.
