Ublox C94-M8P User manual

C94-M8P
u-blox RTK Application Board Package
User Guide
Abstract
This document describes the structure and use of the C94-M8P RTK
application board package and provides information for evaluating
and testing u-blox NEO-M8P high precision positioning modules.
www.u-blox.com
UBX-15031066 - R07

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Document Information
Title
C94-M8P
Subtitle
u-blox RTK Application Board Package
Document type
User Guide
Document number
UBX-15031066
Revision and date
R07
07-Jul-2017
Document status
Early Production Information
Document status explanation
Objective Specification
Document contains target values. Revised and supplementary data will be published later.
Advance Information
Document contains data based on early testing. Revised and supplementary data will be published later.
Early Production Information
Document contains data from product verification. Revised and supplementary data may be published later.
Production Information
Document contains the final product specification.
This document applies to the following products:
Product name
Type number
Firmware/FLASH version
PCN reference
C94-M8P
C94-M8P-1-10
FLASH FW3.01 HPG1.40
UBX-17023320
C94-M8P
C94-M8P-1-11
FLASH FW3.01 HPG1.40
N/A
C94-M8P
C94-M8P-2-10
FLASH FW3.01 HPG1.40
UBX-17023320
C94-M8P
C94-M8P-2-11
FLASH FW3.01 HPG1.40
N/A
C94-M8P
C94-M8P-3-10
FLASH FW3.01 HPG1.40
UBX-17023320
C94-M8P
C94-M8P-3-11
FLASH FW3.01 HPG1.40
N/A
C94-M8P
C94-M8P-4-10
FLASH FW3.01 HPG1.40
UBX-17023320
C94-M8P
C94-M8P-4-11
FLASH FW3.01 HPG1.40
N/A
u-blox reserves all rights to this document and the information contained herein. Products, names, logos and designs described herein
may in whole or in part be subject to intellectual property rights. Reproduction, use, modification or disclosure to third parties of this
document or any part thereof without the express permission of u-blox is strictly prohibited.
The information contained herein is provided “as is” and u-blox assumes no liability for the use of the information. No warranty, either
express or implied, is given, including but not limited, with respect to the accuracy, correctness, reliability and fitness for a particular
purpose of the information. This document may be revised by u-blox at any time. For most recent documents, please visit
www.u-blox.com.
Copyright © 2017, u-blox AG

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Preface
Using this guide
This guide assumes, the user has basic computer skills and is familiar with the Windows Graphical User Interface
(GUI) and GNSS receiver environments.
The following symbols are used in the document to highlight information:
A warning symbol indicates actions that could negatively impact or damage the device.
An index finger points out key information pertaining to device operation and performance.
Warnings and certifications
CAUTION! IN THE UNLIKELY EVENT OF A FAILURE IN THE INTERNAL PROTECTION
CIRCUITRY THERE IS A RISK OF AN EXPLOSION WHEN CHARGING FULLY OR
PARTIALLY DISCHARGED BATTERIES. REPLACE THE BATTERY IF IT NO LONGER
HAS SUFFICIENT CHARGE FOR UNIT OPERATION. CONTROL THE BATTERY BEFORE
USING IF THE DEVICE HAS NOT BEEN OPERATED FOR AN EXTENDED PERIOD OF
TIME.
Products marked with this lead-free symbol on the product label comply with the
“Directive 2002/95/EC and Directive 2011/65/EU of the European Parliament and the
Council on the Restriction of Use of certain Hazardous Substances in Electrical and
Electronic Equipment” (RoHS).
C94-M8P application board is RoHS compliant.

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Contents
Preface ................................................................................................................................3
Using this guide............................................................................................................................................... 3
Warnings and certifications ............................................................................................................................. 3
Contents..............................................................................................................................4
1Introduction..................................................................................................................7
1.1 Overview .............................................................................................................................................. 7
1.2 C94-M8P package ................................................................................................................................ 7
1.3 Software requirements ......................................................................................................................... 7
1.4 System requirements ............................................................................................................................ 7
2Specification .................................................................................................................8
3Getting started .............................................................................................................9
3.1 Software installation ............................................................................................................................. 9
3.2 NEO-M8P and radio modem firmware .................................................................................................. 9
3.3 Hardware installation.......................................................................................................................... 10
3.3.1 GNSS antenna considerations...................................................................................................... 10
4Configuration .............................................................................................................11
4.1 GNSS constellation configuration........................................................................................................ 11
4.2 Static RTK configuration ..................................................................................................................... 11
4.2.1 Base station operation................................................................................................................. 12
4.2.2 Specifying a fixed position ........................................................................................................... 12
4.2.3 Using the self survey-in facility..................................................................................................... 12
4.2.4 Configuring RTCM messages....................................................................................................... 14
4.2.5 NEO-M8P UART settings for the Base .......................................................................................... 16
4.2.6 Rover configuration ..................................................................................................................... 16
4.2.7 NEO-M8P UART settings for the Rover ........................................................................................ 17
4.2.8 Navigation rates supported with standard RTK ............................................................................ 17
4.3 Moving baseline RTK Configuration.................................................................................................... 17
4.3.1 Base station operation................................................................................................................. 17
4.3.2 NEO-M8P UART settings for Base ................................................................................................ 21
4.3.3 Navigation rates supported with moving baseline operation ........................................................ 22
4.3.4 Rover with moving baseline......................................................................................................... 23
4.3.5 Message Latency ......................................................................................................................... 23
5Operation....................................................................................................................24
5.1 Standard RTK mode............................................................................................................................ 24
5.1.1 Base station in operation ............................................................................................................. 24
5.1.2 Rover in operation ....................................................................................................................... 24

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5.2 Moving baseline mode ....................................................................................................................... 25
5.2.1 Base station in operation ............................................................................................................. 25
5.2.2 Rover in operation ....................................................................................................................... 26
5.3 Monitoring the quality of the RTCM stream........................................................................................ 27
5.3.1 Moving baseline .......................................................................................................................... 28
6Evaluation interfaces .................................................................................................29
6.1 RS232/UART Interface ........................................................................................................................ 29
6.2 USB interface...................................................................................................................................... 29
6.3 J8 connector....................................................................................................................................... 29
6.4 Battery connector ............................................................................................................................... 30
6.5 LED..................................................................................................................................................... 30
6.6 Antenna connectors ........................................................................................................................... 30
6.6.1 Radio antenna connector ............................................................................................................ 30
6.6.2 GNSS antenna connector ............................................................................................................ 31
6.7 Wired serial RTCM3 connection between Base and Rover................................................................... 31
7Block diagram.............................................................................................................32
8Board layout ...............................................................................................................33
9Schematic....................................................................................................................34
Appendix ..........................................................................................................................35
AGlossary ......................................................................................................................35
BRadio communication link configuration .................................................................35
B.1 Serial console terminal installation ...................................................................................................... 38
CUpdating C94 radio modem firmware ......................................................................39
C.1 Updating procedure............................................................................................................................ 40
Please download the correct firmware for your C94 variant from the u-blox GitHub website:
https://github.com/u-blox/C94-application-board-radio-firmware/ ................................................................. 40
There are two parts to the firmware, a Boot loader (BL) and the Firmware itself (FW). ................................... 40
DNotes on FW3.01 HPG1.40 .........................................................................................41
ENotes on hardware ....................................................................................................41
E.1 For C94 radio firmware not in current production low latency firmware as indicated in Table 9:......... 41
E.2 For C94 radio firmware that is current production low latency firmware as indicated in Table 9: ........ 42
E.3 C94 Variants -00 ................................................................................................................................ 42
E.3.1 Overview ..................................................................................................................................... 42
E.3.2 Connectors.................................................................................................................................. 42
E.3.3 Dimensions.................................................................................................................................. 43
FHardware modification..............................................................................................44

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Related documents...........................................................................................................46
Revision history................................................................................................................46
Contact..............................................................................................................................47

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1Introduction
1.1 Overview
The C94-M8P application board package provides the means for efficient integration and evaluation of
NEO-M8P, u-blox’s M8 high precision GNSS modules.
The NEO-M8P module series introduces the concept of a “Rover” and a “Base Station”. By using a correction
data stream from the Base Station, the Rover can output its relative position with stunning cm-level accuracy in
good environments.
The C94-M8P board integrates the NEO-M8P-2 module with both Base Station and Rover functionality. The
C94-M8P includes a UHF radio link, allowing for easy setup and fast prototyping. The board also provides
connector pins, enabling a simple wired connection or communication alternatives using u-blox cellular and
short-range technologies.
The C94-M8P application board package comes in four variants, each with an individually configured radio link
to meet different radio frequency requirements in different regions:
C94-M8P-1-10/11 for China (433 MHz)
C94-M8P-2-10/11 for USA and Canada (915 MHz)
C94-M8P-3-10/11 or C94-M8P-3-10 for Europe (433 MHz)
C94-M8P-4-10/11 for Japan (920 MHz)
A label showing the application variant (ordering code) is located at the top-right corner of the board. For
information about variants with the old board version (C94-M8P-1-00, C94-M8P-2-00 and C94-M8P-3-00) refer
to Appendix E.3.
1.2 C94-M8P package
The C94-M8P package includes:
2 application boards (both with a NEO-M8P-2 module)
2 external UHF antennas
2 external active GNSS antennas
2 antenna ground planes
2 USB cables
A RF-shield is attached on the top of the radio modem.
A plastic enclosure is attached on the top of the GNSS module. The purpose of the enclosure is to prevent
airflow affecting TCXO performance.
1.3 Software requirements
To comply with the instructions and examples in this document, the following software is required:
The latest version of u-center for Windows (currently version 8.26). You can download it from
https://www.u-blox.com/en/product/c94-m8p
Serial console terminal, for example Putty
1.4 System requirements
The following system requirements are required to follow the instructions and examples in this document:
PC with USB interface
Operating system: Windows Vista onwards (x86 and x64 versions)
GNSS USB drivers are automatically installed when installing u-center.

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2Specification
Parameter
Specification
Interfaces
1 USB port for GNSS data and power supply
1 RS232, for radio link configuration
Connection pins for UART communication (e.g. C027), 3.3 V
SMA connector
External GNSS antenna and UHF antenna
Dimensions
75 mm x 55 mm
Weight
35 g
Power Supply
5 V via USB or externally powered by battery (5.05 mm pitch 2-pin, 3.7 V –20 V) powered
1 battery connector
Normal Operating temperature
-40 °C to +65 °C
Table 1: C94-M8P application board specification

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3Getting started
3.1 Software installation
The latest version of u-center is needed for the examples and procedures described in this document. Internet
access is also required during the software installation to ensure that the most up-to-date components are
installed on your system. After installation, the u-center application can be found in the”u-blox” folder in the
Start->Program menu.
3.2 NEO-M8P and radio modem firmware
Before starting evaluation, check that the application boards are using the latest firmware for both the NEO-M8P
and radio modem modules.
If you have received C94-M8P-E PCB variants these units will have the latest HPG1.40 firmware on the NEO-M8P
and the latest production radio modem firmware. If you are intending to use a wired RTCM3 serial connection,
the radio firmware will not need updating.
The following points describe the update rates possible using wireless or wired connection modes.
The NEO-M8P used in wireless connection mode will operate at up to 4 Hz (GPS only), 3 Hz (Dual
constellation) for standard RTK operation and 1 Hz for the moving baseline (MB) modes. However, the
maximum rate the radio can transmit is range and environment dependent. It is recommended in
standard RTK mode that the Base is run at 1 Hz while the Rover is run at a higher rate if needed.
The NEO-M8P used in wired connection mode will operate at up to 5 Hz (Dual constellation) and 8 Hz
(GPS only) in standard RTK mode. For moving baseline mode with M8P firmware HPG1.40, this reduces
to 4 Hz (Dual constellation and GPS only).
The latest NEO-M8P firmware is available on the u-blox web site. To find the NEO-M8P firmware variant use the
MON-VER message as shown in section 5.2.6 (Figure 25) of the u-center User Guide [4]. For updating the M8P
firmware, follow the steps described in section 8.1 in the u-center User Guide [4].
Note the following points when updating the NEO-M8P firmware:
All the changes in the M8P configuration are lost when the firmware is updated. The Base and Rover
must be re-configured after updating.
Do not have more than one application board connected to your computer while updating
The M8P UART baud rate and the radio modem baud rate will need to be matched if the C94 radio
firmware is updated from the earlier delivered radio modem firmware. The current production radio
modem firmware defaults to 19200 Baud and the M8P UART speed will need this setting and not 9600
baud as used in the earlier radio modem firmware. Use the M8P CFG-PRT UART command as shown in
section 4.2.4.
The radio modem firmware needs to be the current production firmware for the C94 variant used. To see if the
C94 radio modem needs a firmware update, check your C94 PCB version and the delivered M8P firmware
version shown in the Table 8 and Table 9.
You can verify the radio modem firmware version by using the AT 'I' command when connected to the radio
modem through the standard 9 Pin D-type serial connector J1. See Appendix B Radio communication link
configuration.
For updating the radio modem firmware, see Appendix C.

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3.3 Hardware installation
To test and evaluate the benefits of u-blox Real Time Kinematic (RTK) technology, two C94-M8P application
boards –“Base”and “Rover”–need to be set up as described below.
Connect the UHF antenna to the SMA connector marked with “UHF”
Connect the GNSS antenna to the SMA connector marked with ”GNSS”
Connect the micro USB cable to the micro USB port on the board (for power and configuration)
Depending on the evaluation purposes, the test connectors may be used differently
The two boards are identical. Select one of the boards to
act as a “Base” and one as a “Rover”.
3.3.1 GNSS antenna considerations
In order to optimize the benefit of u-blox Real Time Kinematic (RTK) technology and achieve high accuracy
performance, the antenna placement is extremely important. The recommendations for the GNSS antenna used
with the system are:
The antenna needs to be placed in an open sky environment with unobstructed sky visibility.
Care should be taken to minimize multipath. If the antenna installation does not provide a natural ground
plane, such as mounting on a car roof, using a seperate ground plane is strongly recommended. This can be
achieved by mounting the antenna on the ground plane (supplied with the package) and placing as far as
possible from nearby buildings or other obstructions.
The ground plane should have a minimum diameter of 10 cm. If better performance is required due to
multipath, then a larger ground plane will improve the performance. Moving to a lower multipath environment
might be required.
For more information, refer to Achieving Centimeter Level Performance with Low Cost Antennas [5].

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4Configuration
The C94-M8P package includes two identical boards featuring u-blox NEO-M8P-2 modules. Configure one as a
Base Station, while the other operates as a Rover. You can configure the boards for either static or moving baseline
RTK functionality.
4.1 GNSS constellation configuration
The NEO-M8P-2 positioning module on the C94-M8P application board is a concurrent GNSS receiver that can
receive and track multiple GNSS systems. The NEO-M8P module is configured by default for concurrent GPS and
GLONASS reception, where both constellations will be used in the RTK solution. For most users this is the optimal
configuration and no further re-configuration is needed. Other configurations available are GPS-only and
GPS+BeiDou reception. A single constellation e.g. GPS-only must be used if the highest RTK update rate (8 Hz)
using a wired RTCM3 connection is required.
If the configuration is changed –the changes need to be made for both boards as Base and Rover should use
the same GNSS systems.
For GNSS module configuration, use the micro-A USB port to connect with a PC running u-center. Once it is
connected, configure the module on u-center (View -> Message View -> UBX-CFG-GNSS) as shown in Figure 1. For
more information, refer to the u-center User Guide [4], and u-blox 8 / u-blox M8 Receiver Description including
Protocol Specification [1].
Always remember to store configuration changes by sending the UBX-CFG-CFG message in u-center, which can
be done with the shortcut, .
Figure 1: Configuration of the NEO-M8P-2 GNSS module on C94-M8P application board
4.2 Static RTK configuration
The board that is selected as the Base Station needs to be configured as described below. Configuring the base
station for moving baseline operation is described in section 4.3.

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4.2.1 Base station operation
When the NEO-M8P functions as a Base Station, the receiver uses its measurements from the available satellites to
broadcast its position and satellite observation data to the rover. The Base Station must be configured with a fixed
position or have completed a survey-in operation before it can output the RTCM reference station position message.
By sending the UBX-CFG-TMODE3 message, the Base Station can be set to operate in a fixed position mode or to
self survey-in its position, depending on the user’s knowledge of the Base Station’s antenna reference position.
When the base station coordinates are fixed the navigation solution type is denoted as type 'TIME'.
Disable NMEA output messages via USB (right mouse click on NMEA title in u-center Message View - select
disable child messages) to enable a fixed TIME mode displayed in u-center.
4.2.2 Specifying a fixed position
In the u-center CFG-TMODE3 dialog, specify 'Fixed Mode' and the Base Station’s antenna reference point with
ECEF or Lat/Lon/Alt coordinates. The corresponding fields are shown in Figure 2 below. The parameter fields allow
coordinate specification up to 0.1 mm resolution. For more information, see the u-blox 8 / u-blox M8 Receiver
Description including Protocol Specification [1].
The accuracy of the specified coordinates will reflect directly in the absolute accuracy of the Rover’s position.
Figure 2: Fixed Position Mode configuration for a Base Station
4.2.3 Using the self survey-in facility
If the coordinates of the Base Station antenna are not known to sufficient accuracy, the Base Station can be
configured to self survey its location. When working in Survey-in Mode the Base Station will determine its own
position by building a weighted mean of all valid 3D position solutions.
The UBX-CFG-TMODE3 message has two fields to fill in for Survey-in Mode as shown in the u-center dialog below
in Figure 3. The first field - “Minimum Observation Time”, defines a minimum amount of observation time
regardless of the actual number of valid fixes that were used for position calculation. Reasonable values range from
one day for applications that require high absolute accuracy, to a few minutes for applications that only require
high relative accuracy.

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The second field, “Required Position Accuracy”, forces the calculated Base station position to be of at least the
given 3D position accuracy. This 3D position accuracy is derived estimate from the survey algorithm. This can be
over-estimated, the actual absolute surveyed in accuracy will be no better than approximately 1 m.
Navigation Rate (UBX-CFB-RATE) should be 1 Hz during Survey-in.
Figure 3: Survey-in configuration for a Base Station
In operation, after both requirements are fulfilled, the Base station finishes the Survey-in mode and enters fixed
mode automatically. The Base operation status from Survey-in to Fixed can be monitored via the UBX-NAV-SVIN
message, as shown in Figure 4.

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Figure 4: Base Station moving from Survey-in Mode to Fixed Mode
Users should be aware that the absolute accuracy derived from a survey in exercise is unlikely to be better than 1 m,
even with the best antenna and sky view combination. If the antenna location is known more precisely users should
use this and preset them using the fixed mode.
The rover location is derived from an offset from the base and hence any inaccuracy in the base coordinates will be
inherited plus the relative position uncertainty of typically less than 2 cm.
4.2.4 Configuring RTCM messages
The GNSS satellite configuration used will directly affect RTCM3 messages selection. The NEO-M8P module uses
GPS+GLONASS by default, otherwise other constellations can be selected if desired. A Base device should select the
RTCM Reference Station coordinates message and satellite observation messages for the configured GNSS
constellations. For example, using the default GPS + GLONASS configuration, RTCM messages 1005 (Reference
Station coordinates message), 1077 (GPS observations), 1087 (GLONASS observations) plus 1230 (GLONASS code-
phase biases) are required. For a GPS + BeiDou GNSS configuration, 1005 (Reference Station coordinates), 1077
(GPS observations) and 1127 (BeiDou observations) are required.
The throughput of the RTCM communications link must be considered with respect to the amount of bytes required
for the enabled RTCM messages and message rates. The C94 radio link has a fixed capacity for the amount of
messages sent through the radio link. If the Base receiver is set to run higher than 1 Hz the messages selected will
be sent over the radio link at higher than 1 Hz. If the message data rate exceeds the radio link capacity, delays will
increase and messages can be lost. This can negatively impact the RTK performance of the Rover to a point where it
will not reach Float/Fixed operation.
RTCM 1230 is required to make GLONASS ambiguity fixing possible. This can be sent at a low rate (eg once
every 10s) to save radio link capacity.
MSM4 observation messages (i.e. 1074 for GPS, 1084 for GLONASS, and 1124 for BeiDou) can be used instead
of MSM7 to reduce the communication bandwidth requirements. For moving baseline only MSM7 messages are
supported. These are 1077 for GPS, 1087 for GLONASS and 1127 for BeiDou.

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The NEO-M8P UART1 port is connected to the radio modem on the application board to transmit the correction
data. Hence the UART1 port must be selected as the source for all RTCM messages. To do this, use the UBX-CFG-
MSG messages as shown in Figure 5 and Figure 6. The following points should be considered when selecting RTCM
message configuration:
A default of 1 Hz Navigation Rate is recommended for the Base and Rover.
It is recommended that RTCM messages should be configured to be output at 1 Hz. The output rate must
match the Base station navigation rate, which is 1 Hz by default.
Individual RTCM messages should be configured at the same rate, except for message 1230.
For customers requiring a higher update than 1 Hz at the Rover, the Rover can be configured for either 5 Hz (Dual
constellation) or 8 Hz (GPS only) maximum rates but the Base must remain at a default of 1 Hz. The update rate of
the RTCM3 messages sent from the Base should remain at 1 Hz and will not affect the accuracy of the Rover. N.B
This is not supported in moving baseline operation.
4.2.4.1 GPS + GLONASS RTCM3 message configuration
Figure 5: For a GPS+GLONASS setup, enable the RTCM messages 1005, 1077, 1087 and 1230 on UART1 port

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4.2.4.2 GPS + BeiDou RTCM3 message configuration
Figure 6 For a GPS + BeiDou setup, enable the RTCM messages 1005, 1077, 1127.
4.2.5 NEO-M8P UART settings for the Base
The GNSS module UART needs to be configured on the Base. Use the UBX-CFG-PRT message to set “Protocol in”to
“none” and “Protocol out” to “RTCM3”, as shown in Figure 7. Make sure you only select "none" for protocol in
and only"RTCM3" for protocol out.
Figure 7: Configuring Base radio link
4.2.6 Rover configuration
In its default state, the Rover will automatically apply the RTCM corrections it receives. When the navigation solution
has converged sufficiently it will enter RTK float mode and assuming circumstances allow for it, eventually reach
RTK fixed mode.

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In order to mitigate position jumps when switching between fixed and float modes the rover can be set to remain in
float mode selected using the message UBX-CFG-DGNSS. In this mode, the Rover will estimate the ambiguities as
float but will not attempt to fix them.
The firmware requires a minimum of five ambiguities to attempt fixing. RTK fixed status can be reached when
either of the following requirements is fulfilled: 1) six satellites from a single constellation are available, or 2)
eight satellites from two different constellations are available.
4.2.7 NEO-M8P UART settings for the Rover
The GNSS module UART needs to be configured on the Rover. Use UBX-CFG-PRT message to set “Protocol in” to
“RTCM3”and “Protocol out”to “none”, as shown in Figure 8. Ensure "none" is selected for protocol out and only
RTCM3 for protocol in.
Figure 8: Configuring Rover radio link
4.2.8 Navigation rates supported with standard RTK
The following navigation rate constraints are advised when using the C94 boards for RTCM correction messages
using the C94 radio modems.
A default of 1 Hz is recommended for the Base and Rover.
The Rover can be configured for either 5 Hz (dual constellation) or 8 Hz (GPS only) maximum rates but the
Base must remain at a default of 1 Hz. The update rate of the RTCM3 messages sent from the Base should
remain at 1 Hz and will not affect the accuracy of the Rover. N.B This is not supported in moving baseline
operation.
4.3 Moving baseline RTK Configuration
A moving baseline (MB) configuration differs from standard RTK in that the base station is not necessarily stationary
and can move relative to the rover receiver. The rover position solution provides the user with a vector describing
the difference between the base and rover locations. This is a useful solution for providing a vehicle attitude or
angular bearing when the receivers are co-located. This section covers the C94 configuration for MB operation.
Either a wired or the wireless (radio modem) data connection is possible between the base and rover receivers. Note
that the maximum achievable update rates are only possible with a wired connection compared to the radio
modem. A wired connection is a good solution for co-located Base and Rover devices.
4.3.1 Base station operation
When the NEO-M8P functions as a Base Station, the receiver uses measurements from all available satellites to
broadcast corrections. The Base Station is configured for MB operation by enabling the RTCM message 4072 and
sending the CFG-TMODE3 message with 'Mode' disabled.
Disabling the fixed mode in CFG-TMODE3 is required to activate the moving baseline feature even if Message
4072 is enabled.

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The CFG-TMODE3 message must be sent even though polling a CFG-TMODE3 message shows the mode is set
to disable upon power-up.
With Message 4072 active, message 1005 is not output even if previously enabled.
A configuration flowchart shown below in Figure 9 details the procedure for enabling the default operation.
Figure 9: Moving baseline configuration flowchart using C94 radio GPS+GLONASS configuration

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For the default GPS + GLONASS GNSS configuration, 4072 (u-blox proprietary MB message), 1077 (GPS
observations), 1087 (GLONASS observations) plus 1230 (GLONASS code-phase biases) are required. N.B. Message
1230 enables GLONASS ambiguities to be fixed. For a GPS + BeiDou GNSS configuration, 4072 (u-blox proprietary
MB message) and 1077 (GPS observations), 1127 (BeiDou observations) are required. N.B. MSM7 messages are
required for all moving baseline cases.
The NEO-M8P UART1 port is connected to the radio modem on the application board to transmit the correction
data. Hence the UART1 port must be selected as the source for all RTCM messages. To do this, use the UBX-CFG-
MSG messages as shown in Figure 10 and Figure 11. The following points should be considered when selecting
RTCM message configuration:-
RTCM message rates should be configured to be output at 1 Hz. The message rate must be the same as the
navigation rate of the Base station, which is 1 Hz by default.
The Base and Rover must be configured to the same Navigation Rate; this should be 1 Hz.
Individual RTCM messages should be configured at the same rate, except for message 1230 that can be
configured at a lower rate, .e.g. once every 10 s.
RTCM 1230 is required to make GLONASS ambiguity fixing possible. This can be sent infrequenctly to save radio
link capacity.
If BeiDou is used, RTCM message 1127 needs to be used instead of 1087 (GLONASS), and RTCM 1230 can be
omitted.
MSG 4072 must be set at the same rate as the GPS/GLONASS observables messages.

C94-M8P - User Guide
UBX-15031066 - R07 Early Production Information Configuration
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4.3.1.1 GPS + GLONASS RTCM3 message configuration
Figure 10: For a GPS+GLONASS setup, enable the RTCM messages 4072, 1077, 1087 and 1230 on UART1 port