Ublox RCB-F9T Use and care manual


RCB-F9T
u-blox RCB-F9T high accuracy timing board
Integration manual
Abstract
This document describes the features and application of RCB-F9T, a multi-
band GNSS timing board offering nanosecond level timing accuracy.
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RCB-F9T-Integration manual
Document information
Title RCB-F9T
Subtitle u-blox RCB-F9T high accuracy timing board
Document type Integration manual
Document number UBX-19003747
Revision and date R04 25-Feb-2020
Document status Early production information
This document applies to the following products:
Product name Type number Firmware version PCN reference
RCB-F9T RCB-F9T-0-01 TIM 2.01 UBX-19057484
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 with respect to, including but not limited 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 © 2020, u-blox AG.
u-blox is a registered trademark of u-blox Holding AG in the EU and other countries.
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Contents
1 Integration manual structure............................................................................................ 5
2 System description...............................................................................................................6
2.1 Overview.................................................................................................................................................... 6
2.1.1 Differential timing.......................................................................................................................... 6
2.2 Architecture..............................................................................................................................................6
2.2.1 Block diagram..................................................................................................................................6
3 Receiver functionality.......................................................................................................... 7
3.1 Receiver configuration........................................................................................................................... 7
3.1.1 Changing the receiver configuration..........................................................................................7
3.1.2 Default GNSS configuration.........................................................................................................7
3.1.3 Default interface settings............................................................................................................ 8
3.1.4 Basic receiver configuration.........................................................................................................8
3.1.5 Differential timing mode configuration..................................................................................... 9
3.1.6 Legacy configuration interface compatibility........................................................................ 12
3.1.7 Navigation configuration............................................................................................................12
3.2 Geofencing..............................................................................................................................................16
3.2.1 Introduction...................................................................................................................................16
3.2.2 Interface......................................................................................................................................... 17
3.2.3 Geofence state evaluation......................................................................................................... 17
3.3 Interfaces................................................................................................................................................17
3.3.1 UART interface............................................................................................................................. 17
3.4 Predefined PIOs.....................................................................................................................................18
3.4.1 RESET_N........................................................................................................................................ 18
3.4.2 TIMEPULSE................................................................................................................................... 18
3.5 Antenna supervisor.............................................................................................................................. 18
3.5.1 Antenna voltage control - ANT_OFF........................................................................................18
3.5.2 Antenna short detection - ANT_SHORT_N............................................................................ 19
3.5.3 Antenna short detection auto recovery..................................................................................20
3.5.4 Antenna open circuit detection - ANT_DETECT................................................................... 20
3.6 Multiple GNSS assistance (MGA)..................................................................................................... 21
3.6.1 Authorization................................................................................................................................ 21
3.6.2 Multiple servers............................................................................................................................21
3.6.3 Preserving information during power-off................................................................................21
3.6.4 AssistNow Online......................................................................................................................... 22
3.7 Clocks and time.....................................................................................................................................25
3.7.1 Receiver local time.......................................................................................................................25
3.7.2 Navigation epochs....................................................................................................................... 26
3.7.3 iTOW timestamps........................................................................................................................26
3.7.4 GNSS times................................................................................................................................... 27
3.7.5 Time validity..................................................................................................................................27
3.7.6 UTC representation..................................................................................................................... 27
3.7.7 Leap seconds................................................................................................................................ 28
3.7.8 Real time clock............................................................................................................................. 29
3.7.9 Date.................................................................................................................................................29
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3.8 Timing functionality............................................................................................................................. 30
3.8.1 Time pulse..................................................................................................................................... 30
3.9 Security................................................................................................................................................... 33
3.9.1 Spoofing detection / monitoring...............................................................................................33
3.9.2 Jamming/interference indicator...............................................................................................34
3.9.3 GNSS receiver integrity.............................................................................................................. 34
3.10 u-blox protocol feature descriptions.............................................................................................. 35
3.10.1 Broadcast navigation data...................................................................................................... 35
3.11 Forcing a receiver reset.....................................................................................................................42
4 Design..................................................................................................................................... 43
4.1 Pin assignment......................................................................................................................................43
4.2 Power supply..........................................................................................................................................43
4.2.1 VCC: Main supply voltage.......................................................................................................... 43
4.2.2 RCB-F9T VCC_ANT: Antenna power supply.......................................................................... 44
4.3 Antenna...................................................................................................................................................44
4.4 EOS/ESD precautions.......................................................................................................................... 45
4.4.1 ESD protection measures.......................................................................................................... 45
4.4.2 EOS precautions...........................................................................................................................46
4.4.3 Safety precautions...................................................................................................................... 46
4.5 Electromagnetic interference on I/O lines.......................................................................................46
4.5.1 General notes on interference issues......................................................................................47
4.5.2 In-band interference mitigation................................................................................................47
4.5.3 Out-of-band interference........................................................................................................... 48
5 Product handling................................................................................................................. 49
5.1 ESD handling precautions.................................................................................................................. 49
Appendix.................................................................................................................................... 50
A RCB-F9T default configurations...........................................................................................................50
B Glossary......................................................................................................................................................50
Related documents................................................................................................................ 52
Revision history.......................................................................................................................53

RCB-F9T-Integration manual
1 Integration manual structure
This document provides a wealth of information to enable a successful design with the RCB-F9T
timing board. The manual is structured according to system, software and hardware aspects.
The first section, "System description" outlines the basics of the RCB-F9T timing board.
The following section "Receiver functionality" provides an exhaustive description of the receiver's
functionality. Beginning with the new configuration concept both existing and new users should read
this section to understand the new messages employed. Most of the following sub-sections should
be familiar to existing users of u-blox positioning products, however some changes are introduced
owing to the new configuration concept.
The sections from "Design" onwards addresses power supply recommendations and provides
information about the RCB-F9T hardware interfaces. An antenna section provides design
information and recommendation for this important component.
The final section addresses the major product handling concerns giving guidance on ESD
precautions.
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manual structure
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2 System description
2.1 Overview
The RCB-F9T timing board enables multi-band GNSS timing in a compact form factor using the
ZED-F9T, the u-blox F9 high accuracy timing module. The ZED-F9T module provides nanosecond
level timing accuracy in both standalone and differential timing modes.
In addition to the ZED-F9T module, the RCB-F9T timing board contains an SMB antenna connector
and 5 V power supply circuitry for an external active multi-band GNSS antenna. The 8-pin, 2.0 mm
pitch pin-header provides powering of the board, UART communications, and two independently
configurable time pulse signals.
2.1.1 Differential timing
The u-blox RCB-F9T high accuracy timing board takes local timing accuracy to the next level with
its differential timing mode.
In differential timing mode correction data is exchanged with other neighboring ZED-F9T timing
receivers via a communication network. In differential timing mode the RCB-F9T can operate either
as a master reference station, or as a slave station.
When RCB-F9T acts as a master reference timing station, it sends RTCM 3.3 differential corrections
to slave receivers.
When RCB-F9T acts as a slave receiver, it receives differential corrections RTCM 3.3 messages and
aligns its time pulse to the master reference station.
2.2 Architecture
The RCB-F9T timing board provides all the necessary RF and baseband processing to enable multi-
band GNSS timing. The block diagram below (Figure 1) shows the key functionality implemented in
the RCB-F9T.
2.2.1 Block diagram
Figure 1: RCB-F9T block diagram
An active antenna is mandatory with the RCB-F9T.
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3 Receiver functionality
This section describes the RCB-F9T operational features and their configuration.
3.1 Receiver configuration
The RCB-F9T is fully configurable with UBX configuration interface keys. The configuration
database in the receiver's RAM holds the current configuration, which is used by the receiver
at run-time. It is constructed on start-up of the receiver from several sources of configuration.
The configuration interface and the available keys are described fully in the RCB-F9T Interface
description [2].
The configuration interface has changed from earlier u-blox positioning receivers. There
is some backwards compatibility, however, users are strongly advised to adopt the
configuration interface described in this document. See legacy UBX-CFG message fields
reference section in the RCB-F9T Interface description [2].
Configuration interface settings are held in a database consisting of separate configuration items.
An item is made up of a pair consisting of a key ID and a value. Related items are grouped together
and identified under a common group name: CFG-GROUP-*; a convention used in u-center and
within this document. Within u-center, a configuration group is identified as "Group name" and the
configuration item is identified as the "item name" under the "Generation 9 Configuration View" -
"Advanced Configuration" view.
The UBX messages available to change or poll the configurations are the UBX-CFG-VALSET, UBX-
CFG-VALGET, and UBX-CFG-VALDEL messages. For more information about these messages and
the configuration keys see the configuration interface section in the RCB-F9T Interface description
[2].
3.1.1 Changing the receiver configuration
All configuration messages, including legacy UBX-CFG messages, will result in a UBX-ACK-ACK
or UBX-ACK-NAK response. If several configuration messages are sent without waiting for this
response then the receiver may pause processing of input messages until processing of a previous
configuration message has been completed. When this happens a warning message "wait for cfg
ACK" will be sent to the host.
3.1.2 Default GNSS configuration
The RCB-F9T default GNSS configuration is set as follows:
• GPS: L1C/A, L2C
• GLONASS: L1OF, L2OF
• Galileo: E1B/C, E5b
• BeiDou: B1I, B2I
• QZSS: L1C/A, L2C
SBAS is also supported but not enabled in the default GNSS configuration. SBAS is not
recommended for timing applications.
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For more information about default configuration, see the RCB-F9T Interface description [2].
3.1.3 Default interface settings
Interface Settings
UART Output 115200 baud, 8 bits, no parity bit, 1 stop bit. NMEA GGA, GLL, GSA, GSV, RMC, VTG, TXT (and
no UBX) messages are output by default.
UART Input 115200 baud, 8 bits, no parity bit, 1 stop bit. UBX, NMEA and RTCM 3.3 messages are enabled
by default.
Table 1: Default configurations
Refer to the u-blox RCB-F9T Interface description [2] for information about further
settings.
By default the RCB-F9T outputs NMEA 4.10 messages that include satellite data for all GNSS bands
being received. This results in a higher-than-before NMEA load output for each navigation period.
Make sure the UART baud rate being used is sufficient for the selected navigation rate and the
number of GNSS signals being received.
3.1.4 Basic receiver configuration
This section summarizes the basic receiver configuration most commonly used.
3.1.4.1 Message output configuration
The rate of NMEA, UBX and RTCM protocol output messages are configurable.
If the rate configuration value is zero, then the corresponding message will not be output. Values
greater than zero indicate how often the message is output.
For periodic output messages the rate relates to the event the message is related to. For example,
the UBX-NAV-PVT (navigation position velocity and time solution) is related to the navigation epoch.
If the rate of this message is set to one (1), it will be output for every navigation epoch. If the rate
is set to two (2), it will be output every other navigation epoch. The rates of the output messages
are individually configurable per communication interface. See the CFG-MSGOUT-* configuration
group.
Some messages, such as UBX-MON-VER, are not periodic and will only be output as an answer to
a poll request.
The UBX-INF-* and NMEA-Standard-TXT information messages are non-periodic output messages
that do not have a message rate configuration. Instead they can be enabled for each communication
interface via the CFG-INFMSG-* configuration group.
All message output is additionally subject to the protocol configuration of the
communication interfaces. Messages of a given protocol will not be output until the protocol
is enabled for output on the interface (see the previous section).
3.1.4.2 GNSS signal configuration
The GNSS constellations and bands are configurable with configuration keys from configuration
group CFG-SIGNAL-*. Each GNSS constellation can be enabled or disabled independently. A GNSS
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constellation is considered to be enabled when the constellation enable key is set and at least one
of the constellation's band keys is enabled.
3.1.5 Differential timing mode configuration
In differential timing mode the RCB-F9T can operate either as a master reference station or as a
slave station. Using the RTCM3 protocol, the master sends timing corrections to the slave via a
communication link enabling the slave to compute its time relative to the master with high accuracy.
This section describes how to configure the RCB-F9T high accuracy timing board as a master
reference station and as slave station. The section begins with a note describing the RTCM protocol
and corresponding supported message types.
3.1.5.1 RTCM corrections
RTCM is a binary data protocol for communication of GNSS correction information. The RCB-F9T
high accuracy timing board supports RTCM as specified by RTCM 10403.3, Differential GNSS
(Global Navigation Satellite Systems) Services – Version 3 (October 7, 2016).
The RTCM specification is currently at version 3.3 and RTCM version 2 messages are not supported
by this standard.
To modify the RTCM input/output settings, see the configuration section in the u-blox RCB-F9T
Interface description [2].
3.1.5.2 List of supported RTCM input messages
Message Description
RTCM 1005 Stationary RTK reference station ARP
RTCM 1077 GPS MSM7
RTCM 1087 GLONASS MSM7
RTCM 1097 Galileo MSM7
RTCM 1127 BeiDou MSM7
RTCM 1230 GLONASS code-phase biases
RTCM 4072.1 Additional reference station information
Table 2: RCB-F9T supported input RTCM version 3.3 messages
3.1.5.3 List of supported RTCM output messages
Message Description
RTCM 1005 Stationary RTK reference station ARP
RTCM 1077 GPS MSM7
RTCM 1087 GLONASS MSM7
RTCM 1097 Galileo MSM7
RTCM 1127 BeiDou MSM7
RTCM 1230 GLONASS code-phase biases
RTCM 4072.1 Additional reference station information
Table 3: RCB-F9T supported output RTCM version 3.3 messages
3.1.5.4 Timing receiver position
Time mode is a special receiver mode where the position of the receiver is known and fixed and only
the time and frequency is calculated using all available satellites. This mode allows for maximum
time accuracy, for single-SV solutions, and also for using the receiver as a stationary reference
station.
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In order to use time mode, the receiver's position must be known as exactly as possible. Errors in the
fixed position will translate into time errors depending on the satellite constellation.
The following procedures can be used to initialize the timing receiver position:
• Using built-in survey-in procedure to estimate the position.
• Entering coordinates independently generated or taken from an accurate position such as a
survey marker.
3.1.5.4.1 Survey-in
Survey-in is a procedure that is carried out prior to entering Time mode. It estimates the receiver
position by building a weighted mean of all valid 3D position solutions.
Two major parameters are required when configuring:
• A minimum observation time defines the minimum observation time independent of the
actual number of fixes used for the position estimate. Values can range from one day for high
accuracy requirements to a few minutes for coarse position determination.
• A 3D position standard deviation defines a limit on the spread of positions that contribute to
the calculated mean.
Survey-in ends when both requirements are successfully met. The Survey-in status can be queried
using the UBX-TIM-SVIN message.
The timing receiver should not be fed RTCM corrections while it is in survey-in mode.
To configure a timing receiver into Survey-in mode (CFG-TMODE-MODE=SURVEY_IN), the following
items are required:
Configuration item Description
CFG-TMODE-MODE Receiver mode (disabled, survey-in or fixed)
CFG-TMODE-SVIN_MIN_DUR Survey-in minimum duration
CFG-TMODE-SVIN_ACC_LIMIT Survey-in position accuracy limit. The accuracy of given coordinates in 0.0001
meters (i.e. value 100 equals 1 cm)
Table 4: Configuration items used for setting a timing receiver into Survey-in mode
Set the configuration items shown above into flash memory to perform a survey-in
procedure automatically upon start-up.
3.1.5.4.2 Fixed position
Here the timing receiver position coordinates are entered manually. Any error in the timing receiver
position will directly translate into timing errors.
To configure into Fixed mode (CFG-TMODE-MODE=FIXED), the following items are relevant:
Once the receiver is set in fixed mode, select the position format to use: either LLH or ECEF with
optional high precision (mm) coordinates compared to the standard cm value.
For example, with CFG-TMODE-POS_TYPE=ECEF the timing receiver antenna position can be
entered to cm precision using CFG-TMODE-ECEF_X, CFG-TMODE-ECEF_Y, CFGTMODE-ECEF_Z.
For high precision (mm) coordinates use CFG-TMODEECEF_X_HP, CFG-TMODE-ECEF_Y_HP, CFG-
TMODE-ECEF_Z_HP. The same applies with corresponding coordinates used with CFG-TMODE-
POS_TYPE=LLH.
If the timing receiver is moved during operation then new position coordinates must be
configured.
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3.1.5.5 Master reference station
When the RCB-F9T high accuracy timing board acts as a master timing station, it sends RTCM 3.3
differential corrections to slave receivers. Corrections are generated after a timing fix calculation in
order to remove the master receiver's clock offset.
3.1.5.5.1 Master reference station: RTCM output configuration
At this point the timing receiver should report a TIME fix, not a 3D fix.
The desired RTCM messages must be selected and configured on UART1 rate 1:
• RTCM 1005 Stationary RTK reference station ARP
• RTCM 1077 GPS MSM7
• RTCM 1088 GLONASS MSM7
• RTCM 1097 Galileo MSM7
• RTCM 1127 BeiDou MSM7
• RTCM 1230 GLONASS code-phase biases
• RTCM 4072 Additional reference station information
The configuration messages for these are shown in the Table 5.
The following configuration items output the recommended messages for a default satellite
constellation setting. Note that these are given for the UART1 interface:
Configuration item Description
CFG-UART1OUTPROT-NMEA CFG-UART1OUTPROT-NMEA to 0
CFG-UART1OUTPROT-RTCM3X CFG-UART1OUTPROT-RTCM3X to 1
CFG-UART1OUTPROT-UBX CFG-UART1OUTPROT-UBX to 0
CFG-MSGOUT-
RTCM_3X_TYPE1005_UART1
Output rate of the RTCM-3X-TYPE1005 message on port UART1: RTCM base
station message
CFG-MSGOUT-
RTCM_3X_TYPE1077_UART1
Output rate of the RTCM-3X-TYPE1077 message on port UART1: RTCM GPS
MSM7
CFG-MSGOUT-
RTCM_3X_TYPE1087_UART1
Output rate of the RTCM-3X-TYPE1087 message on port UART1: RTCM GLONASS
MSM7
CFG-MSGOUT-
RTCM_3X_TYPE1097_UART1
Output rate of the RTCM-3X-TYPE1097 message on port UART1: RTCM Galileo
MSM7
CFG-MSGOUT-
RTCM_3X_TYPE1127_UART1
Output rate of the RTCM-3X-TYPE1127 message on port UART1: RTCM Additional
reference station information
CFG-MSGOUT-
RTCM_3X_TYPE1230_UART1
Output rate of the RTCM-3X-TYPE1230 message on port UART1: RTCM GLONASS
code-phase biases
CFG-MSGOUT-
RTCM_3X_TYPE4072_1_UART1
Output rate of the RTCM-3X-TYPE4072.1 message on port UART1: RTCM
Additional reference station information
Table 5: Configuration items used for setting a master reference station
3.1.5.6 Slave station
When the RCB-F9T acts as a slave receiver, it receives differential corrections RTCM 3.3 messages
from a master reference station and aligns its time pulse to it.
Connect the slave receiver to the reference server or to the NTRIP server. When the slave receives
the configured RTCM correction stream, it will automatically start using the corrections.
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Reception of RTCM 4072.1 is required to start using differential correction data.
3.1.6 Legacy configuration interface compatibility
There is some backwards-compatibility for the legacy UBX-CFG configuration messages. It is
strongly recommended to adopt the new configuration interface, as the legacy configuration
messages support will be removed in the future.
See Legacy UBX-CFG message fields reference section in the RCB-F9T Interface description [2].
3.1.7 Navigation configuration
This section presents various configuration options related to the navigation engine. These options
can be configured through various configuration groups, such as CFG-NAVSPG-*, CFG-ODO-*, and
CFG-MOT-*.
3.1.7.1 Platform settings
u-blox receivers support different dynamic platform models (see in the table below) to adjust
the navigation engine to the expected application environment. These platform settings can be
changed dynamically without performing a power cycle or reset. The settings improve the receiver's
interpretation of the measurements and thus provide a more accurate position output. Setting the
receiver to an unsuitable platform model for the given application environment is likely to result in
a loss of receiver performance and position accuracy.
The dynamic platform model can be configured through the CFG-NAVSPG-DYNMODEL
configuration item. The supported dynamic platform models and their details can be seen in Table
6 and Table 7 below.
Platform Description
Portable (default) Applications with low acceleration, e.g. portable devices. Suitable for most situations.
Stationary Used in timing applications (antenna must be stationary) or other stationary applications.
Velocity restricted to 0 m/s. Zero dynamics assumed.
Pedestrian Applications with low acceleration and speed, e.g. how a pedestrian would move. Low
acceleration assumed.
Automotive Used for applications with equivalent dynamics to those of a passenger car. Low vertical
acceleration assumed.
At sea Recommended for applications at sea, with zero vertical velocity. Zero vertical velocity assumed.
Sea level assumed.
Airborne <1g Used for applications with a higher dynamic range and greater vertical acceleration than a
passenger car. No 2D position fixes supported.
Airborne <2g Recommended for typical airborne environments. No 2D position fixes supported.
Airborne <4g Only recommended for extremely dynamic environments. No 2D position fixes supported.
Wrist Only recommended for wrist-worn applications. Receiver will filter out arm motion.
Table 6: Dynamic platform models
Platform Max altitude [m] Max horizontal
velocity [m/s]
Max vertical velocity
[m/s]
Sanity check type Max
position
deviation
Portable 12000 310 50 Altitude and velocity Medium
Stationary 9000 10 6 Altitude and velocity Small
Pedestrian 9000 30 20 Altitude and velocity Small
Automotive 6000 100 15 Altitude and velocity Medium
At sea 500 25 5 Altitude and velocity Medium
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Platform Max altitude [m] Max horizontal
velocity [m/s]
Max vertical velocity
[m/s]
Sanity check type Max
position
deviation
Airborne <1g 50000 100 100 Altitude Large
Airborne <2g 50000 250 100 Altitude Large
Airborne <4g 50000 500 100 Altitude Large
Wrist 9000 30 20 Altitude and velocity Medium
Table 7: Dynamic platform model details
3.1.7.2 Navigation input filters
The navigation input filters in CFG-NAVSPG-* configuration group provide the input data of the
navigation engine.
Configuration item Description
CFG-NAVSPG-FIXMODE By default, the receiver calculates a 3D position fix if possible but reverts to 2D
position if necessary (auto 2D/3D). The receiver can be forced to only calculate 2D
(2D only) or 3D (3D only) positions.
CFG-NAVSPG-CONSTR_ALT, CFG-
NAVSPG-CONSTR_ALTVAR
The fixed altitude is used if fixMode is set to 2D only. A variance greater than zero
must also be supplied.
CFG-NAVSPG-INFIL_MINELEV Minimum elevation of a satellite above the horizon in order to be used in the
navigation solution. Low elevation satellites may provide degraded accuracy, due to
the long signal path through the atmosphere.
CFG-NAVSPG-INFIL_NCNOTHRS,
CFG-NAVSPG-INFIL_CNOTHRS
A navigation solution will only be attempted if there are at least the given number of
SVs with signals at least as strong as the given threshold.
Table 8: Navigation input filter parameters
If the receiver only has three SVs for calculating a position, the navigation algorithm uses a constant
altitude to compensate for the missing fourth SV. When a SV is lost after a successful 3D fix (min.
four SVs available), the altitude is kept constant at the last known value. This is called a 2D fix.
u-blox receivers do not calculate any navigation solution with less than three SVs.
3.1.7.3 Navigation output filters
The result of a navigation solution is initially classified by the fix type (as detailed in the fixType
field of UBX-NAV-PVT message). This distinguishes between failures to obtain a fix at all ("No Fix")
and cases where a fix has been achieved, which are further subdivided into specific types of fixes
(e.g. 2D, 3D, dead reckoning).
The RCB-F9T firmware does not support the dead reckoning position fix type.
Where a fix has been achieved, a check is made to determine whether the fix should be classified as
valid or not. A fix is only valid if it passes the navigation output filters as defined in CFG-NAVSPG-
OUTFIL. In particular, both PDOP and accuracy values must be below the respective limits.
Important: Users are recommended to check the gnssFixOK flag in the UBX-NAV-PVT or
the NMEA valid flag. Fixes not marked valid should not be used.
UBX-NAV-STATUS message also reports whether a fix is valid in the gpsFixOK flag. These
messages have only been retained for backwards compatibility and users are recommended to use
the UBX-NAV-PVT message.
3.1.7.3.1 Speed (3D) low-pass filter
The CFG-ODO-OUTLPVEL configuration item offers the possibility to activate a speed (3D) low-pass
filter. The output of the speed low-pass filter is published in the UBX-NAV-VELNED message (speed
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field). The filtering level can be set via the CFG-ODO-VELLPGAIN configuration item and must be
comprised between 0 (heavy low-pass filtering) and 255 (weak low-pass filtering).
The internal filter gain is computed as a function of speed. Therefore, the level as defined in
the CFG-ODO-VELLPGAIN configuration item defines the nominal filtering level for speeds
below 5 m/s.
3.1.7.3.2 Course over ground low-pass filter
The CFG-ODO-OUTLPCOG configuration item offers the possibility to activate a course over ground
low-pass filter when the speed is below 8 m/s. The output of the course over ground (also named
heading of motion 2D) low-pass filter is published in the UBX-NAV-PVT message (headMot field),
UBX-NAV-VELNED message (heading field), NMEA-RMC message (cog field) and NMEA-VTG
message (cogt field). The filtering level can be set via the CFG-ODO-COGLPGAIN configuration item
and must be comprised between 0 (heavy low-pass filtering) and 255 (weak low-pass filtering).
The filtering level as defined in the CFG-ODO-COGLPGAIN configuration item defines the
filter gain for speeds below 8 m/s. If the speed is higher than 8 m/s, no course over ground
low-pass filtering is performed.
3.1.7.3.3 Low-speed course over ground filter
The CFG-ODO-USE_COG activates this feature and the CFG-ODO-COGMAXSPEED, CFG-ODO-
COGMAXPOSACC configuration items offer the possibility to configure a low-speed course over
ground filter (also named heading of motion 2D). This filter derives the course over ground from
position at very low speed. The output of the low-speed course over ground filter is published in the
UBX-NAV-PVT message (headMot field), UBX-NAV-VELNED message (heading field), NMEA-RMC
message (cog field) and NMEA-VTG message (cogt field). If the low-speed course over ground filter
is not configured, then the course over ground is computed as described in section Freezing the
course over ground.
3.1.7.4 Static hold
Static hold mode allows the navigation algorithms to decrease the noise in the position output when
the velocity is below a pre-defined "Static Hold Threshold". This reduces the position wander caused
by environmental factors such as multi-path and improves position accuracy especially in stationary
applications. By default, static hold mode is disabled.
If the speed drops below the defined "Static Hold Threshold", the static hold mode will be activated.
Once static hold mode has been entered, the position output is kept static and the velocity is set to
zero until there is evidence of movement again. Such evidence can be velocity, acceleration, changes
of the valid flag (e.g. position accuracy estimate exceeding the position accuracy mask, see also
section Navigation output filters), position displacement, etc.
The CFG-MOT-GNSSDIST_THRS configuration item additionally allows for configuration of
distance threshold. If the estimated position is farther away from the static hold position than this
threshold, static mode will be quit. The CFG-MOT-GNSSSPEED_THRS configuration item allows you
to set a speed that the static hold will release.
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Figure 2: Position publication in static hold mode
Figure 3: Flowchart of the static hold mode
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3.1.7.5 Freezing the course over ground
If the low-speed course over ground filter is deactivated or inactive (see section Low-speed course
over ground filter), the receiver derives the course over ground from the GNSS velocity information.
If the velocity cannot be calculated with sufficient accuracy (e.g., with bad signals) or if the absolute
speed value is very low (under 0.1 m/s) then the course over ground value becomes inaccurate too.
In this case the course over ground value is frozen, i.e. the previous value is kept and its accuracy
is degraded over time. These frozen values will not be output in the NMEA messages NMEA-RMC
and NMEA-VTG unless the NMEA protocol is explicitly configured to do so (see NMEA protocol
configuration in the RCB-F9T Interface description [2]).
Figure 4: Flowchart of the course over ground freezing
3.2 Geofencing
3.2.1 Introduction
Figure 5: Geofence
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The geofencing feature allows for the configuration of up to four circular areas (geofences) on the
Earth's surface. The receiver will then evaluate for each of these areas whether the current position
lies within the area or not and signal the state via UBX messaging and PIO toggling.
3.2.2 Interface
Geofencing can be configured using the CFG-GEOFENCE-* configuration group. The geofence
evaluation is active whenever there is at least one geofence configured.
The current state of each geofence plus the combined state is output in UBX-NAV-GEOFENCE with
every navigation epoch.
Additionally the user can configure the receiver to output the combined geofence state on a physical
pin (assigned to a PIO being used for geofence state indication).
3.2.3 Geofence state evaluation
With every navigation epoch the receiver will evaluate the current solution's position versus the
configured geofences. There are three possible outcomes for each geofence:
•Inside - The position is inside the geofence with the configured confidence level
•Outside - The position lies outside of the geofence with the configured confidence level
•Unknown - There is no valid position solution or the position uncertainty does not allow for
unambiguous state evaluation
The position solution uncertainty (standard deviation) is multiplied with the configured confidence
sigma level number and taken into account when evaluating the geofence state (red circle in figure
below).
Figure 6: Geofence states
The combined state for all geofences is evaluated as the combination (Union) of all geofences:
•Inside - The position lies inside of at least one geofence
•Outside - The position lies outside of all geofences
•Unknown - All remaining states
3.3 Interfaces
RCB-F9T provides a UART interface for communication with a host CPU.
It is important to isolate interface pins when the RCB-F9T VCC is removed. They can be
allowed to float or connected to a high impedance.
3.3.1 UART interface
RCB-F9T includes one UART port.
UART can be used for host interface. It supports a configurable baud rate and protocol selection.
The default baud rate is 115200 baud. To prevent buffering problems it is recommended
not to run at a lower baud rate than 38400 baud.
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3.4 Predefined PIOs
In addition to the communication ports, there are some predefined PIOs provided by RCB-F9T to
interact with the receiver. These PIOs are described in this chapter.
3.4.1 RESET_N
The RCB-F9T provides the ability to reset the receiver. The RESET_N pin is an input-only pin with an
internal pull-up resistor. Driving RESET_N low for at least 100 ms will trigger a cold start.
The RESET_N pin will delete all information and trigger a cold start. It should only be used
as a recovery option.
3.4.2 TIMEPULSE
The RCB-F9T provides time pulse signals on the TIMEPULSE and TIMEPULSE 2 pins.
Shared TIMEPULSE2 and SAFEBOOT_N signals should be implemented maintaining the
possibility to pull the SAFEBOOT_N pin low in the application.
More information about the Timepulse feature, its possibility's and configuration can be
found in the chapter Time pulse
3.5 Antenna supervisor
The RCB-F9T includes an active antenna supervisor that provides the means to check the antenna
for open and short circuits and to shut off the antenna supply if a short circuit is detected. Once
enabled, the active antenna supervisor produces status messages, reporting in NMEA and/or UBX
protocol.
The RCB-F9T active antenna supervisor block diagram is shown in the Figure 1
The antenna supervisor is monitoring active antenna current consumption and based on that
antenna open and short circuits are detected:
• Antenna open: Current consumption less than 16 mA (typical value)
• Antenna short circuit: Current consumption is more than 215 mA (typical value)
The antenna supervisor can be configured through the CFG-HW-ANT_* configuration items. The
current configuration of the active antenna supervisor can also be checked by polling the related
CFG-HW_ANT_* configuration items.
The current active antenna status can be determined by polling the UBX-MON-RF message. If an
antenna is connected, the initial state after power-up is “Active Antenna OK" in the u-center UBX-
MON-RF view.
The active antenna supervisor is enabled by default in the RCB-F9T.
3.5.1 Antenna voltage control - ANT_OFF
Enable the antenna short detection by setting the configuration item CFG-HW-
ANT_CFG_SHORTDET to true (1).
Result:
• UBX-MON-RF in u-center: Antenna status = OK. Antenna power status = ON
• ANT_OFF = active high to disable an external antenna therefore the pin is low to enable an
external antenna.
• ANT_SHORT_N = active low to detect a short therefore the pin is high (PIO pull up enabled to be
pulled low if shorted)
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Start-up message at power up if configuration is stored:
$GNTXT,01,01,02,ANTSUPERV=AC SD *37
$GNTXT,01,01,02,ANTSTATUS=INIT*3B
$GNTXT,01,01,02,ANTSTATUS=OK*25
ANTSUPERV=AC SD (Antenna control and short detection activated)
Then if shorted (ANT_SHORT_N pulled low):
• UBX-MON-RF in u-center: Antenna status = SHORT. Antenna power status = ON (auto power
down is not enabled = off by default)
$GNTXT,01,01,02,ANTSTATUS=SHORT*73
• ANT_OFF = active high therefore still low (still enabled as auto power down is not enabled)
After a detected antenna short, the reported antenna status will keep on being reported as
shorted. If the antenna short detection auto recovery is enabled, then the antenna status
can recover after a timeout. To recover the antenna status immediately, a power cycle is
required or configuring off and on again the antenna short detection functionality.
The antenna voltage control is enabled by default in the RCB-F9T.
3.5.2 Antenna short detection - ANT_SHORT_N
To set short circuit detect ON:
CFG-HW-ANT_CFG_SHORTDET = 1
Result:
• MON-RF in u-center: Antenna status = OK. Antenna power status = ON
• ANT_OFF = active high to disable an external antenna therefore the pin is low to enable an
external antenna.
• ANT_SHORT_N = active low to detect a short therefore the pin is high (PIO pull up enabled to be
pulled low if shorted)
Start up message at power up if configuration is stored:
$GNTXT,01,01,02,ANTSUPERV=AC SD *37
$GNTXT,01,01,02,ANTSTATUS=INIT*3B
$GNTXT,01,01,02,ANTSTATUS=OK*25
ANTSUPERV=AC SD (Antenna control and short detection activated)
Then if shorted (ANT_SHORT_N pulled low)
• MON-RF in u-center: Antenna status = SHORT. Antenna power status = ON (Antenna power
control powerdown when short has not been enabled = off by default)
• $GNTXT,01,01,02,ANTSTATUS=SHORT*73
• ANT_OFF = active high therefore still low (still enabled as auto power down is not enabled)
The antenna short detection is enabled by default in the RCB-F9T.
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Power off and on required to clear short condition report. Or turn feature off an on again.
3.5.3 Antenna short detection auto recovery
Enable the antenna short detection auto recovery by setting the configuration item CFG-HW-
ANT_CFG_RECOVER to true (1).
Result:
• UBX-MON-RF in u-center: Antenna status = OK. Antenna power status = ON
• ANT_OFF = active high there for the PIO is low to enable an external antenna
• ANT_SHORT_N = high (PIO pull up enabled to be pulled low if shorted)
Start-up message at power up if configuration is stored:
$GNTXT,01,01,02,ANTSUPERV=AC SD PDoS SR*3E
$GNTXT,01,01,02,ANTSTATUS=INIT*3B
$GNTXT,01,01,02,ANTSTATUS=OK*25
ANTSUPERV=AC SD PDoS SR (indicates short circuit recovery added - SR)
Then if antenna is shorted (ANT_SHORT_N pulled low):
•$GNTXT,01,01,02,ANTSTATUS=SHORT*73
• UBX-MON-RF in u-center: Antenna status = SHORT. Antenna power status = OFF
• ANT_OFF = high (to disable - active high)
After a time out period receiver will re-test the short condition by enabling ANT_OFF = LOW
If a short is not present it will report antenna condition is ok:
$GNTXT,01,01,02,ANTSTATUS=OK*25
MON-RF in u-center: Antenna status = OK. Antenna power status = ON
The antenna short detection auto recovery is enabled by default in the RCB-F9T.
3.5.4 Antenna open circuit detection - ANT_DETECT
Enable the antenna open circuit detection by setting the configuration item CFG-HW-
ANT_CFG_OPENDET to true (1).
Result:
• UBX-MON-RF in u-center: Antenna status = OK. Antenna power status = ON
• ANT_OFF = active high therefore PIO is low to enable external antenna
• ANT_SHORT_N = active low therefore PIO is high (PIO pull up enabled to be pulled low if
shorted)
• ANT_DETECT = active high therefore PIO is high (PIO pull up enabled to be pulled low if antenna
not detected)
Start-up message at power up if configuration is stored:
$GNTXT,01,01,02,ANTSUPERV=AC SD OD PDoS SR*15
$GNTXT,01,01,02,ANTSTATUS=INIT*3B
$GNTXT,01,01,02,ANTSTATUS=OK*25
ANTSUPERV=AC SD OD PDoS SR (indicates open circuit detection added - OD)
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