UBX-16018104 - R05
Early Production Information
Troubleshooting
Page 19 of 23
10
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, 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 side is set to RS232 and not USB. In USB Mode the RS232 pins on the
DB9 connector are switched off.
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.
After installing USB driver for the first time by connecting EVK-M8QSAM to PC with USB cable, the
cursor on PC starts to jump around the screen
The syndrome is caused when the NMEA 0183 GNSS serial data is misinterpreted as a mouse data by the serial
port enumerator (serenum.sys), resulting in erratic mouse cursor activity. Change the USB/RS232 switch to
RS232 can help to recover the control of the cursor and disable the enumerator setting in the Windows Device
Manager / Ports (COM&LPT) / USB Serial Port (COMxx) / Port Settings / Advanced...
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.
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.
