EVK-M8U - User Guide
UBX-15023994 - R01
Advance Information
Troubleshooting
Page 22 of 26
11
Troubleshooting
My application (e.g. u-center) does not receive anything
Make sure that the USB cable is properly connected to the evaluation unit and the PC and USB drivers are
installed correctly. By default, the evaluation unit outputs NMEA protocol on Serial Port 1 at 9600 Bd and 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, GNSS receivers based on
u-blox M8 GNSS technology
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).
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 inaccurate 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 inaccurate 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 if the configured thresholds (i.e. P
Accuracy Mask and PDOP) are exceeded.
TTFF times at startup are much longer than specified
At startup (after the first position fix), the GNSS receiver performs an RTC calibration to have an accurate internal
time source. A calibrated RTC is required to achieve minimal startup time.
Before shutting down the receiver externally, check the status in MON-HW in field “Real Time Clock Status”. Do
not shut down the receiver if the RTC is not calibrated.
The EVK-M8U 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
