UM001 Vn 100 User Manual (um001)

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Embedded Navigation Solutions

VN-100 User Manual

Firmware v2.1.0.0
Document Revision 2.23

UM001

Document Information
Title
Subtitle
Document Type
Document Number
Document Status

VN-100 User Manual
Inertial Navigation Modules
User Manual
UM001 v2.23
Released

VectorNav Technical Documentation
In addition to our product-specific technical data sheets, the following manuals are available to assist
VectorNav customers in product design and development.





VN-100 User Manual: The user manual provides a high-level overview of product specific
information for each of our inertial sensors. Further detailed information regarding hardware
integration and application specific use can be found in the separate documentation listed
below.
Hardware Integration Manual: This manual provides hardware design instructions and
recommendations on how to integrate our inertial sensors into your product.
Application Notes: This set of documents provides a more detailed overview of how to utilize
many different features and capabilities offered by our products, designed to enhance
performance and usability in a wide range of application-specific scenarios.

Document Symbols
The following symbols are used to highlight important information within the manual:
The information symbol points to important information within the manual.
The warning symbol points to crucial information or actions that should be followed to avoid
reduced performance or damage to the navigation module.

Technical Support
Our website provides a large repository of technical information regarding our navigation sensors. A list
of the available documents can be found at the following address:
http://www.vectornav.com/support
If you have technical problems or cannot find the information that you need in the provided documents,
please contact our support team by email or phone. Our engineering team is committed to providing the
required support necessary to ensure that you are successful with the design, integration, and operation
of our embedded navigation sensors.

Technical Support Contact Info
Email: support@vectornav.com

Phone: +1.512.772.3615

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Table of Contents
1 Introduction

1.1 PRODUCT DESCRIPTION

1.2 FACTORY CALIBRATION

1.3 OPERATION OVERVIEW

1.4 PACKAGING OPTIONS

1.5 VN-100 PRODUCT CODES

2 Specifications
2.1 VN-100 SURFACE-MOUNT SENSOR (SMD) ELECTRICAL

9
9

2.2 VN-100 RUGGED ELECTRICAL

2.3 VN-100 SURFACE-MOUNT SENSOR (SMD) DIMENSIONS

2.4 VN-100 RUGGED DIMENSIONS

2.5 ABSOLUTE MAXIMUM RATINGS

2.6 SENSOR COORDINATE SYSTEM

3 VN-100 Software Architecture

3.1 IMU SUBSYSTEM

3.2 NAVSTATE SUBSYSTEM

3.3 NAVFILTER SUBSYSTEM

3.4 VECTOR PROCESSING ENGINE

3.5 COMMUNICATION INTERFACE

3.6 COMMUNICATION PROTOCOL

3.7 SYSTEM ERROR CODES

3.8 CHECKSUM / CRC

4 User Configurable Binary Output Messages

4.1 AVAILABLE OUTPUT TYPES

4.2 CONFIGURING THE OUTPUT TYPES

4.3 SERIAL OUTPUT MESSAGE FORMAT

4.4 BINARY GROUP 1 – COMMON OUTPUTS

4.5 BINARY GROUP 2 – TIME OUTPUTS

4.6 BINARY GROUP 3 – IMU OUTPUTS

4.7 BINARY GROUP 5 – ATTITUDE OUTPUTS

5 System Module
5.1 COMMANDS

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53
53

5.2 CONFIGURATION REGISTERS

5.3 STATUS REGISTERS

5.4 FACTORY DEFAULTS

5.5 COMMAND PROMPT

6 IMU Subsystem

6.1 IMU MEASUREMENT REGISTERS

6.2 IMU CONFIGURATION REGISTERS

6.3 FACTORY DEFAULTS

6.4 COMMAND PROMPT

7 Attitude Subsystem

7.1 COMMANDS

7.2 MEASUREMENT REGISTERS

7.3 CONFIGURATION REGISTERS

100

8 Hard/Soft Iron Estimator Subsystem

101

8.1 CONFIGURATION REGISTERS

101

8.2 STATUS REGISTERS

102

8.3 FACTORY DEFAULTS

103

8.4 COMMAND PROMPT

104

9 Velocity Aiding

107

9.1 OVERVIEW

107

9.2 CONFIGURATION REGISTERS

111

9.3 STATUS REGISTERS

112

9.4 INPUT MEASUREMENTS

113

9.5 FACTORY DEFAULTS

114

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Introduction

1.1

Product Description

The VN-100 is a miniature surface mount high-performance Inertial Measurement Unit (IMU) and Attitude
Heading Reference System (AHRS). Incorporating the latest solid-state MEMS sensor technology, the VN100 combines a set of 3-axis accelerometers, 3-axis gyroscopes, 3-axis magnetometers, a barometric
pressure sensor and a 32-bit processor. The VN-100 is considered both an IMU in that it can output
acceleration, angular rate, and magnetic measurements along the X, Y, & Z axes of the sensor as well as
an AHRS in that it can output filtered attitude estimates of the sensor with respect to a local coordinate
frame.

1.2

Factory Calibration

MEMS inertial sensors are subject to several common sources of error: bias, scale factor, misalignments,
temperature dependencies, and gyro g-sensitivity. All VN-100 sensors undergo a rigorous calibration
process at the VectorNav factory to minimize these error sources. Compensation parameters calculated
during these calibrations are stored on each individual sensor and digitally applied to the real-time
measurements.


1.3

Thermal Calibration – this option extends the calibration process over multiple temperatures to
ensure performance specifications are met over the full operating temperature range of -40 C to
+85 C.

Operation Overview

The VN-100 has a built-in microcontroller that runs a quaternion based Extended Kalman Filter (EKF),
which provides estimates of both the attitude of the sensor as well as the real-time gyro biases. VectorNav
uses a quaternion based attitude filter because it is continuous over a full 360 degree range of motion
such that there are no limitations on the angles it can compute. However, the VN-100 also has a built-in
capability to output yaw, pitch, and roll angles from the VN-100, in which the sensor automatically
converts from quaternions to the desired attitude parameter. Outputs from the VN-100 include:







Attitude:
o Yaw, Pitch, & Roll
o Quaternions
o Direction Cosine Matrix
Angular Rates:
o Bias-Compensated
o Calibrated X, Y, & Z Gyro Measurements
Acceleration:
o Calibrated X, Y, & Z Measurements
Magnetic:
o Calibrated X, Y, & Z Measurements
Barometric Pressure

The VN-100 EKF relies on comparing measurements from the onboard inertial sensors to two reference
vectors in calculating the attitude estimates: gravity down and magnetic North. Measurements from the

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three-axis accelerometer are compared to the expected magnitude and direction of gravity in determining
the pitch and roll angles while measurements from the three-axis magnetometer are compared to the
expected magnitude and direction of Earth’s background magnetic field in determining the heading angle
(i.e. yaw angle with respect to Magnetic North).
The VN-100 Kalman Filter is based on the assumption that the accelerometer measurements should only
be measuring gravity down. If the sensor is subject to dynamic motion that induces accelerations, the
pitch and roll estimates will be subject to increased errors. These measurements can be accounted and
compensated for by using the VN-100 Velocity Aiding Feature (See Section 10 for more information).

The VN-100 filter relies on comparing the onboard magnetic measurements to Earth’s background
magnetic field in determining its heading angle. Common objects such as batteries, electronics, cars,
rebar in concrete, and other ferrous materials can bias and distort the background magnetic field leading
to increased errors. These measurements can be accounted and compensated for by using the VN-100
Hard/Soft Iron Algorithms (See Section 9 for more information).

VectorNav has developed a suite of tools called the Vector Processing Engine (VPE™), which are builtinto the VN-100 and minimize the effects of these disturbances; however, it is not possible to obtain
absolute heading accuracies better than 2 degrees over any extended period of time when relying on
magnetometer measurements.

The VN-100 EKF also integrates measurements from the three-axis gyroscopes to provide faster and
smoother attitude estimates as well as angular rate measurements. Gyroscopes of all kinds are subject
to bias instabilities, in which the zero readings of the gyro will drift over time to due to inherent noise
properties of the gyro itself. The VN-100 EKF uses the accelerometer and magnetometer measurements
to continuously estimate the gyro bias, such that the report angular rates are compensated for this drift.

1.4

Packaging Options

The VN-100 is available in two different configurations; a 30-pin surface mount package (VN-100 SMD)
and an aluminum encased module (VN-100 Rugged). The VN-100 surface mount package is well suited
for customers looking to integrate the VN-100 sensor at the electronics level while the VN-100 Rugged
provides a precision enclosure with mounting tabs and alignment holes for a more off-the-shelf solution.

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1.4.1

Surface-Mount Package

For embedded applications, the VN-100 is available in a
miniature surface-mount package.

Features





Small Size: 22 x 24 x 3 mm
Single Power Supply: 3.2 to 5.5 V
Communication Interface: Serial TTL & SPI
Low Power Requirement: < 105 mW @ 3.3V

1.4.2

Rugged Package

The VN-100 Rugged consists of the VN-100 sensor installed
and calibrated in a robust precision aluminum enclosure.

Features







Precision aluminum enclosure
Locking 10-pin connector
Mounting tabs with alignment holes
Compact Size: 36 x 33 x 9 mm
Single Power Supply: 4.5 to 5.5 V
Communication Interface: Serial RS-232 & TTL

1.4.3

Surface Mount Development Kit

The VN-100 Development Kit provides the VN-100
surface-mount sensor installed onto a small PCB,
providing easy access to all of the features and pins on
the VN-100. Communication with the VN-100 is
provided by USB and RS-232 serial communication
ports. A 30-pin header provides easy access to each of
the critical pins. The VN-100 Development Kit also
includes all of the necessary cabling, documentation,
and support software.

Features






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Pre-installed VN-100 Sensor
Onboard USB->Serial converter
Onboard TTL->RS-232 converter
30-pin 0.1” header for access to VN-100 pins
Power supply jack – 5V (Can be powered from
USB)
7



Board Size: 76 x 76 x 14 mm

1.4.4

VN-100 Rugged Development Kit

The VN-100 Rugged Development Kit includes the
VN-100 Rugged sensor along with all of the
necessary cabling required for operation. Two
cables are provided in each Development Kit: one
custom cable for RS-232 communication and a
second custom cable with a built in USB converter.
The Development Kit also includes all of the relevant
documentation and support software.

Features








1.5

VN-100 Rugged Sensor
10 ft RS-232 cable
10 ft USB connector cable
Cable Connection Tool
CD w/Software Development Kit
User Manual, Quick Start Guide
Documentation
Carrying Case

VN-100 Product Codes
VN-100 Options

Item Code
VN-100S
VN-100T
VN-100S-DEV
VN-100T-DEV
VN-100S-CR
VN-100T-CR
VN-100S-CR-DEV
VN-100T-CR-DEV
VN-C100-0310
VN-C100-0410

Sensor Packaging
Surface Mount Device
Surface Mount Device
Surface Mount Development Kit
Surface Mount Development Kit
Rugged Module
Rugged Module
Rugged Development Kit
Rugged Development Kit
VN-100 Rugged USB Adapter Cable
VN-100 Rugged Serial Adapter Cable

Calibration Option
Standard at 25C
Thermal -40C to +85C
Standard at 25C
Thermal -40C to +85C
Standard at 25C
Thermal -40C to +85C
Standard at 25C
Thermal -40C to +85C
N/A
N/A

Product Type
IMU/AHRS
IMU/AHRS
IMU/AHRS
IMU/AHRS
IMU/AHRS
IMU/AHRS
IMU/AHRS
IMU/AHRS
Cable
Cable

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Specifications

2.1

VN-100 Surface-Mount Sensor (SMD) Electrical
Pin assignments (top down view)

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VN-100 SMD Pin Assignments
Pin
1
2
3
4
5
6
7

Pin Name
GND
GND
GND
GND
TX2
RX2
RESTORE

Type
Supply
Supply
Supply
Supply
Output
Input
Input

8
9
10
11

RESV
SYNC_OUT
VIN
ENABLE

N/A
Output
Supply
Input

12
13
14
15
16
17
18
19
20
21

TX1
RX1
RESV
RESV
SPI_SCK
SPI_MOSI
GND
SPI_MISO
RESV
NRST

Output
Input
N/A
N/A
Input
Input
Supply
Output
N/A
Input

22
23
24
25
26
26
28
29
30

SYNC_IN
SPI_CS
RESV
RESV
RESV
RESV
GND
RESV
GND

Input
Input
N/A
N/A
N/A
N/A
Supply
N/A
Supply

Description
Ground.
Ground.
Ground.
Ground.
Serial UART #2 data output. (sensor)
Serial UART #2 data input. (sensor)
Normally used to zero (tare) the attitude. To tare, pulse high for at least 1 μs.
During power on or device reset, holding this pin high will cause the module to
restore the default factory settings.
As a result, the pin cannot be used for tare until at least 5 ms after a
power on or reset.
Internally held low with 10k resistor.
Reserved for internal use. Do not connect.
Time synchronization output signal.
3.2 - 5.5 V input.
Leave high for normal operation. Pull low to enter sleep mode. Internally pulled
high with pull-up resistor.
Serial UART #1 data output. (sensor)
Serial UART #1 data input. (sensor)
Reserved for internal use. Do not connect.
Reserved for internal use. Do not connect.
SPI clock.
SPI input.
Ground.
SPI output.
Reserved for internal use. Do not connect.
Microcontroller reset line. Pull low for > 20 μs to reset MCU. Internally pulled
high with 10k.
Time synchronization input signal.
SPI slave select.
Reserved for internal use. Do not connect.
Reserved for internal use. Do not connect.
Reserved for internal use. Do not connect.
Reserved for internal use. Do not connect.
Ground.
Reserved for internal use. Do not connect.
Ground.

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2.1.1 VN-100 SMD Power Supply
The minimum operating supply voltage is 3.2V and the absolute maximum is 5.5V.

2.1.2

VN-100 SMD Serial (UART) Interface

The serial interface on the VN-100 operates with 3V TTL logic.
Serial I/O Specifications
Specification
Input low level voltage
Input high level voltage
Output low voltage
Output high voltage

2.1.3

Min
-0.5 V
2V
0V
2.4 V

Typical

Max
0.8 V
5.5 V
0.4 V
3.0 V

VN-100 SMD Serial Peripheral Interface (SPI)
Serial I/O Specifications
Specification
Input low level voltage
Input high level voltage
Output low voltage
Output high voltage
Clock Frequency
Close Rise/Fall Time

2.1.4

Min
-0.5 V
2V
0V
2.4 V

Typical

8 MHz

Max
0.8 V
5.5 V
0.4 V
3.0 V
16 MHz
8 ns

VN-100 SMD Reset, SyncIn/Out, and Other General I/O Pins
NRST Specifications
Specification
Input low level voltage
Input high level voltage
Weak pull-up equivalent resistor
NRST pulse width

Min
-0.5 V
2V
30 kΩ
20 μs

Typical

40 kΩ

Max
0.8 V
5.5 V
50 kΩ

SyncIn Specifications
Specification
Input low level voltage
Input high level voltage
Pulse Width

Min
-0.5 V
2V
100 ns

Typical

Max
0.8 V
5.5 V

Typical

Max
0.4 V
3.0 V
125 ns
125 ns
1 kHz

SyncOut Specifications
Specification
Output low voltage
Output high voltage
Output high to low fall time
Output low to high rise time
Output Frequency

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Min
0V
2.4 V

1 Hz

2.2

VN-100 Rugged Electrical
VN-100 Rugged Pin Assignments

Pin
1
2
3
4

Pin Name
VCC
TX1
RX1
SYNC_OUT

5
6

GND
TARE/RESTORE

SYNC_IN

8
9
10

TX2_TTL
RX2_TTL
RESV

Description
+4.5V to +5.5V
RS-232 voltage levels data output from the sensor. (Serial UART #1)
RS-232 voltage levels data input to the sensor. (Serial UART #1)
Output signal used for synchronization purposes. Software configurable
to pulse when ADC, IMU, or attitude measurements are available.
Ground
Input signal used to zero the attitude of the sensor. If high at reset, the
device will restore to factory default state. Internally held low with 10k
resistor.
Input signal for synchronization purposes. Software configurable to
either synchronize the measurements or the output with an external
device.
Serial UART #2 data output from the device at TTL voltage level (3V).
Serial UART #2 data into the device at TTL voltage level (3V).
This pin should be left unconnected.

VN-100 Rugged External Connector

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2.2.1

VN-100 Rugged Power Supply

The power supply input for the VN-100 Rugged is 4.5 to 5.5 V DC.

2.2.2

VN-100 Rugged Serial UART Interface
Serial I/O Specifications
Specification
Input low level voltage
Input high level voltage
Output low voltage
Output high voltage
Output resistance
Data rate
Pulse slew

2.2.3

Min
-25 V

Typical

-5.0 V
5.0 V
300 Ω

-5.4 V
5.5 V
10 MΩ

Max
25 V

1 Mbps
300 ns

VN-100 Rugged Reset, SyncIn/Out, and Other General I/O Pins
NRST Specifications
Specification
Input low level voltage
Input high level voltage
Weak pull-up equivalent resistor
NRST pulse width

Min
-0.5 V
2V
30 kΩ
20 μs

Typical

40 kΩ

Max
0.8 V
5.5 V
50 kΩ

SyncIn Specifications
Specification
Input low level voltage
Input high level voltage
Pulse Width

Min
-0.5V
2V
100 ns

Typical

Max
0.8V
5.5V

Typical

Max
0.4 V
3.0 V
125 ns
125 ns
1 kHz

SyncOut Specifications
Specification
Output low voltage
Output high voltage
Output high to low fall time
Output low to high rise time
Output Frequency

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Min
0V
2.4 V

1 Hz

2.3

VN-100 Surface-Mount Sensor (SMD) Dimensions

* Measurements are in inches

2.4

VN-100 Rugged Dimensions

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2.4.1

Rugged Connector Type

The main connector used on the VN-100 Rugged is a 10-pin Harwin M80-5001042. The mating connector
used on the cable assemblies provided by VectorNav for use with the VN-100 Rugged is a Harwin M804861005.

2.5

Absolute Maximum Ratings
SMD Absolute Maximum Ratings
Specification
Input Voltage
Operating Temperature
Storage Temperature

Min
-0.3 V
-40 C
-40 C

Max
5.5 V
85 C
85 C

Rugged Absolute Maximum Ratings
Specification
Input Voltage
Operating Temperature
Storage Temperature

2.6
2.6.1

Min
-0.3 V
-40 C
-40 C

Max
5.5 V
85 C
85 C

Sensor Coordinate System
Sensor Coordinate Frame

The VN-100 uses a right-handed coordinate system. A positive yaw angle is defined as a positive righthanded rotation around the Z-axis. A positive pitch angle is defined as a positive right-handed rotation
around the Y-axis. A positive roll angle is defined as a positive right-handed rotation around the X-axis.
The axes direction with respect to the VN-100 module is shown in the figure below.
VN-100 Coordinate System

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2.6.2

North-East-Down Frame

The VN-100 velocity estimates can be output in the North-East-Down (NED) coordinate frame defined as
follows (NX, NY, NZ):





Right-handed, Cartesian, non-inertial, geodetic frame with origin located at the surface of Earth
(WGS84 ellipsoid);
Positive X-axis points towards North, tangent to WGS84 ellipsoid;
Positive Y-axis points towards East, tangent to WGS84 ellipsoid;
Positive Z-axis points down into the ground completing the right-handed system.

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VN-100 Software Architecture

The software architecture internal to the VN-100 includes four separate subsystems. These subsystems
are the IMU, the NavState, the NavFilter, and the Communication Interface. The high-level functions
performed by these subsystems are outlined below. This chapter describes these functions performed by
these subsystems in more detail and describes which of the various measurement outputs originate from
each of these corresponding subsystems.
VN-100 Software Architecture

IMU

NavState

NavFilter

Comm
Interface

Downsamples
IMU sensors to
800 Hz

Calculates
orientation at
400Hz

Vector
Processing
Engine

Serial ASCII

Applies Factory
Calibration

Computes delta
angles

AHRS Kalman
Filter

Serial Binary

Applies User
Calibration

Computes delta
velocity

Hard/Soft Iron
Estimator

SPI

Applies User
Reference
Frame Rotation

World Magnetic
Model

Serial Command
Prompt

Applies User
Low-Pass
Filtering

World Gravity
Model

Applies Onboard
Calibration

Timestamps
Measurements

3.1

IMU Subsystem

The IMU subsystem runs at the highest system rate, described from this point forward as the IMU Rate
(defaults to 800 Hz). It is responsible for collecting the raw IMU measurements, applying a factory, user,
and dynamic calibration to these measurements, and optionally filtering the individual sensor
measurements for output. The coning and sculling integrals also are calculated by the IMU subsystem at
the full IMU Rate. The IMU subsystem is also responsible for time stamping the IMU measurements to
internal system time, and relative to the SyncIn signal.

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3.1.1

Magnetometer
Magnetometer IMU Measurements
External
Magnetometer
Data

Raw
Magnetometer
Data

3.1.2

User
Magnetometer
Compensation
(Register 23)

User Reference
Frame Rotation
(Register 26)

Factory
Calibration

User Low-Pass
Filtering
(Uncompensated)
(Register 85)

User Low-Pass
Filtering
(Compensated)
(Register 85)

Uncompensated
Magnetometer
(uncompMag)

Onboard Hard/
Soft Iron
Compensation
(Register 44+47)

Compensated
Magnetometer
(magBody)

Accelerometer
Accelerometer IMU Measurements

Raw
Accelerometer
Data

3.1.3

Factory
Calibration

User
Accelerometer
Compensation
(Register 25)

User Reference
Frame Rotation
(Register 26)

User Low-Pass
Filtering
(Uncompensated)
(Register 85)

User Low-Pass
Filtering
(Compensated)
(Register 85)

Uncompensated
Accelerometer
(uncompAccel)

Accelerometer
Filter Bias
Compensation

Compensated
Accelerometer
(accelBody)

Gyro
Gyro IMU Measurements

Raw Gyro Data

3.1.4

Factory
Calibration

User Gyro
Compensation
(Register 84)

User Reference
Frame Rotation
(Register 26)

User Low-Pass
Filtering
(Uncompensated)
(Register 85)

User Low-Pass
Filtering
(Compensated)
(Register 85)

Uncompensated
Angular Rate
(uncompGyro)

Gyro Filter Bias
Compensation

Compensated
Angular Rate
(angularRate)

Raw IMU Measurements

The raw IMU measurements are collected from the internal MEMS at the highest rate available for each
individual sensor. For the gyro and accelerometer, the measurements are down-sampled to the IMU Rate.

3.1.5

Factory Calibration

Each VN-100 sensor is tested at the factory at multiple known angular rates, accelerations, and magnetic
field strengths to determine each sensor’s unique bias, scale factor, axis alignment, and temperature
dependence. The calibration coefficients required to remove these unwanted errors are permanently
stored in flash memory on each sensor. At the IMU Rate, these calibration coefficients are applied to the
raw IMU measurements, to correct for and remove these known measurement errors. For thermally
calibrated units the onboard temperature sensor is used to remove the measurement temperature
dependence. The output of the factory calibration stage is referred to as the calibrated (but uncompensated) IMU measurements.

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3.1.6

User Calibration

The VN-100 provides the user with the ability to apply a separate user calibration to remove additional
bias, scale factor, and axis misalignments. The user calibration is applied after the factory calibration, and
can be used to optionally fine tune the calibration for each of the individual sensors. The user calibration
is optional and in most cases not required for normal operation.

3.1.7

User Reference Frame Rotation

The user reference frame rotation provides the user with the ability to apply a rigid body rotation to each
of the sensor outputs. This can be used to transform the coordinate system of the onboard sensors into
any other coordinate frame of the user’s choice. Since this transformation is applied to the IMU
measurements prior to their use in the onboard attitude estimation algorithms, applying a user reference
frame rotation will not only change the output coordinates for the IMU measurements, it will also change
the IMU body frame for all subsequent attitude estimation calculations.
A write settings and reset command must be issued after setting the Reference Frame Rotation Register
before coordinate transformation will be applied.

3.1.8

User Low-Pass Filtering

The VN-100 also provides a means (see Register 85) to apply low-pass filtering to the output compensated
IMU measurements. It is important to note that the user low-pass filtering only applies to the output
compensated IMU measurements. All onboard Kalman filters in the NavFilter subsystem always use the
unfiltered IMU measurements after the User Reference Frame Rotation (Register 26) has been applied.
As such the onboard Kalman filtering will not be affected by the user low-pass filter settings. The user
low-pass filtering can be used to down-sample the output IMU measurements to ensure that information
is not lost when the IMU measurements are sampled by the user at a lower rate than the internal IMU
Rate.

3.1.9

Timestamp Measurements

All onboard measurements captured by the IMU subsystem are time stamped relative to several internal
timing events. These events include the monotonically increasing system time (time since startup), the
time since the last SyncIn event, and the time since the last GPS PPS pulse. These timestamps are recorded
with microsecond resolution and ~10 microsecond accuracy relative to the onboard temperature
compensated crystal oscillator. The onboard oscillator has a timing accuracy of ~20ppm over the
temperature range of -40C to 80C.

3.1.10 Coning & Sculling
The IMU subsystem is also responsible for computing and accumulating the coning and sculling integrals.
These integrals track the delta angle and delta velocity accumulated from one time step to another. The
coning and sculling integrals are reset each time the delta angle and/or delta velocity are outputted
(asynchronously) or polled from the delta theta and velocity register (Register 80). Between output and
polling events, the coning and sculling integration are performed by the IMU subsystem at the IMU Rate.

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3.2

NavState Subsystem

The NavState subsystem generates a continuous reliable stream of low-latency, low-jitter state outputs
at a rate fixed to the IMU sample rate. The state outputs include any output such as attitude, position,
and velocity, which are not directly measureable by the IMU and hence must be estimated by the onboard
Kalman filters. The NavState runs immediately after, and in sync with the IMU subsystem, at a rate
divisible into the IMU Rate. This rate is referred to as the NavState Rate (default 800 Hz). The NavState
decouples the rate at which the state outputs are made available to the user from the rate at which they
are being estimated by the onboard Kalman filters. This is very important for many applications which
depend on low-latency, low-jitter attitude, position, and velocity measurements as inputs to their control
loops. The NavState guarantees the output of new updated state information at a rate fixed to the IMU
Rate with very low latency and output jitter. The NavState also provides the ability for the VN-100 to
output estimated states at rates faster than the rate of the onboard Kalman filters, which may be affected
by system load and input measurements availability.

3.2.1

NavState Measurements

The measurements shown below are calculated by the NavState subsystem and are made available at the
NavState Rate (default 800 Hz).
NavState Outputs
Attitude
(Yaw, Pitch, Roll, Quaternion, DCM)
Position
(LLA, ECEF)
Velocity
(NED, ECEF, Body)
Delta Angle (Available at full IMU rate)
Delta Velocity (Available at full IMU rate)

3.3

NavFilter Subsystem

The NavFilter subsystem consists of the INS Kalman filter, the Vector Processing Engine (VPE), and its
collection of other Kalman filters and calculations that run at a lower rate than the NavState. Most high
level states such as the estimated attitude, position, and velocity are passed from the NavFilter to the
NavState, and as such are made available to the user at the NavState rate. There are a handful of outputs
however that will only update at the rate of the NavFilter, some of which are listed below.
NavFilter Outputs
Attitude Uncertainty
Position & Velocity Uncertainty
Gyro & Accel Filter Biases
Mag & Accel Disturbance Estimation
Onboard Magnetic Hard & Soft Iron Estimation
World Magnetic & Gravity Model

3.3.1

INS Kalman Filter

The INS Kalman filter consists of an Extended Kalman filter which nominally runs at the NavFilter rate
(default 200 Hz). The INS Kalman filter uses the accelerometer, gyro, GPS, and (at startup) the
magnetometer to simultaneously estimate the full quaternion based attitude solution, the position and

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velocity, as well as the time varying gyro, accelerometer, and barometric pressure sensor biases. The
output of the INS Kalman filter is passed to the NavState, allowing for the attitude, position, and velocity
to be made available at the higher fixed rate of the NavState.

3.3.2

Vector Processing Engine

3.3.3

AHRS Kalman Filter

The AHRS Kalman filter consists of an EKF which nominally runs at the NavFilter Rate (default 200 Hz). The
AHRS Kalman filter simultaneously estimates the full quaternion based attitude as well as the time varying
gyro bias. The quaternion based attitude estimation eliminates any potential gimbal lock issues incurred
at high pitch angles, which can be problematic for Euler-angle based AHRS algorithms. The real-time
estimation of the gyro bias allows for the removal of small perturbations in the gyro bias which occur over
time due to random walk.

3.3.4

Hard/Soft Iron Estimator

The NavFilter subsystem also includes a separate EKF which provides real-time estimation of the local
magnetic hard and soft iron distortions. Hard and soft iron distortions are local magnetic field distortions
created by nearby ferrous material which moves with the sensor (attached to the same vehicle or rigidbody as the sensor). These ferrous materials distort the direction and magnitude of the local measured
magnetic field, thus negatively impacting the ability of an AHRS to reliably and accurately estimate
heading based on the magnetometer measurements. To remove the unwanted effect of these materials,
a hard & soft iron calibration needs to be performed which requires rotating the sensor around in multiple
circles while collecting magnetic data for off-line calculation of the magnetic hard & soft iron calibration
coefficients. This calibration can be very time consuming, and might not be possible for some applications.
The onboard hard/soft iron estimator runs in the background without requiring any user intervention. For
many applications this simplifies the process for the end user, and allows for operation in environments
where the hard/soft iron may change slowly over time. While the onboard hard/soft iron estimator runs
in the background by default, it can be turned off by the user if desired in the Magnetic Calibration Control
Register.

3.3.5

World Magnetic Model

The world magnetic model (WMM) is a large spatial-scale representation of the Earth’s magnetic field.
The internal model used on the VN-100 is consistent with the current WMM2016 model which consist of
a spherical-harmonic expansion of the magnetic potential of the geomagnetic field generated in the
Earth’s core. By default the world magnetic model on the VN-100 is turned off, allowing the user to
directly set the reference magnetic field strength. Alternatively the world magnetic model can be
manually used to calculate the magnetic field strength for a given latitude, longitude, altitude, and date
which is then subsequently used as the fixed magnetic field reference strength. Control of the world
magnetic model is performed using the Reference Vector Configuration Register.

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3.3.6

World Gravity Model

The world gravity model (WGM) is a large spatial-scale representation of the Earth’s gravity potential as a
function of position on the globe. The internal model used on the VN-100 is consistent with the Earth
Gravity Model (EGM96), which consist of a spherical-harmonic expansion of the Earth’s geopotential. By
default the world gravity model on the VN-100 is turned off, allowing the user to directly set the reference
gravity vector. Control of the world gravity model is performed using the Reference Vector Configuration
Register.

3.4

Vector Processing Engine

The Vector Processing Engine (VPE) is a collection of sophisticated algorithms which provide real-time
monitoring and simultaneous estimation of the attitude as well as the uncertainty of the input
measurements used by the attitude estimation algorithm. By estimating its own input measurement
uncertainty the VPE is capable of providing significantly improved performance when compared to a
traditional statically tuned EKF AHRS attitude estimation algorithm. The estimated measurement
uncertainty is used too in real-time at the NavFilter rate (default 200 Hz) adaptively tune the attitude
estimation Kalman filter. This adaptive tuning eliminates the need in most cases for the user to perform
any custom filter tuning for different applications. It also provides extremely good disturbance rejection
capabilities, enabling the VN-100 in most cases to reliably estimate attitude even in the presence of
vibration, short-term accelerations, and some forms of magnetic disturbances.

3.4.1

Adaptive Filtering

The VPE employs adaptive filtering techniques to significantly reduce the effect of high frequency
disturbances in both magnetic and acceleration. Prior to entering the attitude filter, the magnetic and
acceleration measurements are digitally filtered to reduce high frequency components typically caused
by electromagnetic interference and vibration. The level of filtering applied to the inputs is dynamically
altered by the VPE in real-time. The VPE calculates the minimal amount of digital filtering required in order
to achieve specified orientation accuracy and stability requirements. By applying only the minimal amount
of filtering necessary, the VPE reduces the amount of delay added to the input signals. For applications
that have very strict latency requirements, the VPE provides the ability to limit the amount of adaptive
filtering performed on each of the input signals.

3.4.2

Adaptive Tuning

Kalman filters employ coefficients that specify the uncertainty in the input measurements which are
typically used as “tuning parameters” to adjust the behavior of the filter. Normally these tuning
parameters have to be adjusted by the engineer to provide adequate performance for a given application.
This tuning process can be ad-hoc, time consuming, and application dependent. The VPE employs adaptive
tuning logic which provides on-line estimation of the uncertainty of each of the input signals during
operation. This uncertainty is then applied directly to the onboard attitude estimation Kalman filter to
correctly account for the uncertainty of the inputs. The adaptive tuning reduces the need for manual filter
tuning.

3.4.3

VPE Heading Modes

The VectorNav VPU provides three separate heading modes. Each mode controls how the VPE interprets
the magnetic measurements to estimate the heading angle. The three modes are described in detail in
the following sections.

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Absolute Heading Mode
In Absolute Heading Mode the VPE will assume that the principal long-term DC component of the
measured magnetic field is directly related to the earth’s magnetic field. As such only short term magnetic
disturbances will be tuned out. This mode is ideal for applications that are free from low frequency (less
than ~ 1Hz) magnetic disturbances and/or require tracking of an absolute heading. Since this mode
assumes that the Earth's magnetic field is the only long-term magnetic field present, it cannot handle
constant long-term magnetic disturbances which are of the same order of magnitude as the Earth's
magnetic field and cannot be compensated for by performing a hard/soft iron calibration. From the
sensor's perspective a constant long-term magnetic disturbance will be indistinguishable from the
contribution due to the Earth's magnetic field, and as such if present it will inevitably result in a loss of
heading accuracy.
If a magnetic disturbance occurs due to an event controlled by the user, such as the switching on/off of
an electric motor, an absolute heading can still be maintained if the device is notified of the presence
of the disturbance.

To correctly track an absolute heading you will need to ensure that the hard/soft iron distortions remains
well characterized.

Absolute Heading Mode Advantages


Provides short-term magnetic disturbance rejection while maintaining absolute tracking of the
heading relative to the fixed Earth.

Absolute Heading Mode Disadvantages



If the magnetic field changes direction relative to the fixed Earth, then its direction will need to
be updated using the reference vector register in order to maintain an accurate heading
reference.
Hard/Soft iron distortions that are not properly accounted for will induce heading errors
proportional to the magnitude of the hard/soft iron distortion. In some cases this could be as high
as 30-40 degrees.

Relative Heading Mode
In Relative Heading mode the VPE makes no assumptions as to the long term stability of the magnetic
field present. In this mode the VPE will attempt to extract what information it reasonably can from the
magnetic measurements in order to maintain an accurate estimate of the gyro bias. The VPE will
constantly monitor the stability of the magnetic field and when it sees that its direction is reasonably
stable, the VPE will maintain a stable heading estimate. Over long periods of time under conditions where
the magnetic field direction changes frequently, in Relative Heading mode it is possible for the VN-100 to
accumulate some error in its reported heading relative to true North. In this mode the VPE will not attempt
to correct for this accumulated heading error.
Relative Heading mode does not assume that the Earth's magnetic field is the only long-term magnetic
field present. As such this mode is capable of handling a much wider range of magnetic field disturbances
while still maintaining a stable attitude solution. Relative Heading mode should be used in situations
where the most important requirement is for the attitude sensor is to maintain a stable attitude solution

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which minimizes the effect of gyro drift while maintaining a stable and accurate pitch and roll solution.
Since the Relative Heading mode assumes that other magnetic disturbances can be present which are
indistinguishable from the Earth's field, Relative Heading mode cannot always ensure that the calculated
heading is always referenced to Earth's magnetic north.
Use the Relative Heading mode for applications where the stability of the estimated heading is more
important than the long-term accuracy relative to true magnetic North. In general, the Relative Heading
mode provides better magnetic disturbance rejection that the Absolute Heading mode.

Relative Heading Mode Advantages



Capable of handling short-term and long-term magnetic interference.
Can handle significant errors in the hard/soft iron while still maintaining a stable heading and gyro
bias estimate.

Relative Heading Mode Disadvantages


Unable to maintain heading estimate relative to true North in environments with frequent longterm magnetic field disturbances.

Indoor Heading Mode
The Indoor Heading mode was designed to meet the needs of applications that require the enhanced
magnetic disturbance rejection capability of the Relative Heading mode, yet desire to maintain an
absolute heading reference over long periods of time. The Indoor Heading mode extends upon the
capabilities of the Relative Heading mode by making certain assumptions as to the origin of the measured
magnetic fields consistent with typical indoor environments.
In any environment the measured magnetic field in 3D space is actually the combination of the Earth’s
magnetic field plus the contribution of other local magnetic fields created by nearby objects containing
ferromagnetic materials. For indoor environments this becomes problematic due to the potential close
proximity to objects such as metal desk and chairs, speakers, rebar in the concrete floor, and other items
which either distort or produce their own magnetic field. The strength of these local magnetic fields are
position dependent, and if the strength is on the same order of magnitude as that of the Earth’s magnetic
field, directly trusting the magnetic measurements to determine heading can lead to inaccurate heading
estimates.
While in Indoor Heading mode the VPE inspects the magnetic measurements over long periods of time,
performing several different tests on each measurement to quantify the likelihood that the measured
field is free of the influence of any position dependent local magnetic fields which would distort the
magnetic field direction. Using this probability the VPE then estimates the most likely direction of the
Earth’s magnetic field and uses this information to correct for the heading error while the device is in
motion.

Indoor Heading Mode Advantages




Capable of handling short-term and long-term magnetic interference
Can handle significant errors in the hard/soft iron while still maintaining a stable heading and
gyro bias estimate.
Capable of maintaining an accurate absolute heading over extended periods of time.

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Indoor Heading Mode Disadvantages


Measurement repeatability may be worse than Relative Mode during periods when the VPE
corrects for known errors in absolute heading.

Overview of Heading Modes
A summary of the different types of disturbances handled by each magnetic mode is summarized in the
table below.
Capabilities
Handle high frequency magnetic
disturbances greater than 1Hz?
Handle constant disturbances lasting
less than a few seconds?
Handle constant disturbances lasting
longer than a few seconds?

3.4.4

Absolute
Heading
Yes

Relative
Heading
Yes

Indoor
Mode
Yes

Yes

Capabilities
Handle high frequency magnetic
disturbances greater than 1Hz?
Handle
constant
disturbances
lasting less than a few seconds?
Handle
constant
disturbances
lasting longer than a few seconds?

VPE Adaptive Filtering and Tuning Settings

The VPE actively employs both adaptive filtering and adaptive tuning techniques to enhance performance
in conditions of dynamic motion and magnetic and acceleration disturbances. The VPE provides the ability
to modify the amount of adaptive filtering and tuning applied on both the magnetometer and the
accelerometer. In many cases the VPE can be used as is without any need to adjust these settings. For
some applications higher performance can be obtained by adjusting the amount of adaptive filtering and
tuning performed on the inputs. For both the magnetometer and the accelerometer the following settings
are provided.

Static Measurement Uncertainty
The static gain adjusts the level of uncertainty associated with either the magnetic or acceleration
measurement when no disturbances are present. The level of uncertainty associated with the
measurement will directly influence the accuracy of the estimated attitude solution. The level of
uncertainty in the measurement will also determine how quickly the attitude filter will correct for errors
in the attitude when they are observed. The lower the uncertainty, the quicker it will correct for observed
errors.




This parameter can be adjusted from 0 to 10.
Zero places no confidence (or infinite uncertainty) in the sensor, thus eliminating its effect on
the attitude solution.
Ten places full confidence (minimal uncertainty) in the sensor and assume that its measurements
are always 100% correct.

Adaptive Tuning Gain
The adaptive tuning stage of the VPE monitors both the magnetic and acceleration measurements over
an extended period of time to estimate the time-varying level of uncertainty in the measurement. The
adaptive tuning gain directly scales either up or down this calculated uncertainty.


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This parameter can be adjusted from 0 to 10.




The minimum value of zero turns off all adaptive tuning.
The maximum value of 10 applies several times the estimated level of uncertainty.

Adaptive Filtering Gain
The adaptive filtering stage of the VPE monitors both the magnetic and acceleration measurements to
determine if large amplitude high frequency disturbances are present. If so then a variable level of filtering
is applied to the inputs in order to reduce the amplitude of the disturbance down to acceptable levels
prior to inputting the measurement into the attitude filter. The advantage of the adaptive filtering is that
it can improve accuracy and eliminate jitter in the output attitude when large amplitude AC disturbances
are present. The disadvantage to filtering is that it will inherently add some delay to the input
measurement. The adaptive filtering gain adjusts the maximum allowed AC disturbance amplitude for the
measurement prior to entering the attitude filter. The larger the allowed disturbance, the less filtering
that will be applied. The smaller the allowed disturbance, the more filtering will be applied.




This parameter can be adjusted from 0 to 10.
The minimum value of zero turns off all adaptive filtering.
The maximum value of 10 will apply maximum filtering.

Keep in mind that regardless of this setting, the adaptive filtering stage will apply only the minimal amount
of filtering necessary to get the job done. As such this parameter provides you with the ability to set the
maximum amount of delay that you are willing to accept in the input measurement.

3.5

Communication Interface

The VN-100 provides two separate communication interfaces on two separate serial ports.

3.5.1

Serial Interface

The serial interface consists of two physically separate bi-directional UARTs. Each UART supports baud
rates from 9600 bps up to a maximum of 921600 bps.
The rugged version includes an onboard TTL to RS-232 level shifter, thus at the 10-pin connector one serial
port is offered with RS-232 voltages levels (Serial 1), while the other serial port (Serial 2) remains at 3V
TTL logic levels.
It is important to note that the ability to update the firmware using the onboard bootloader is only
supported on the serial port 1 interface. It is highly recommended that if serial port 1 is not used for
normal operation, a means of accessing it is designed into the product to support future firmware
updates.

3.5.2

SPI Interface

The SPI interface consists of a standard 4-wire synchronous serial data link which is capable of high data
rates up to 16 Mbps. The VN-100 operates as slave on the bus enabled by the master using the slave
select (SPI_CS) line. See the Basic Communication chapter for more information on the operation of the
SPI interface.

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3.6

Communication Protocol

The VN-100 utilizes a simple command based communication protocol for the serial interface. An ASCII
protocol is used for command and register polling, and an optional binary interface is provided for
streaming high speed real-time sensor measurements.

3.6.1

Serial ASCII

On the serial interface a full ASCII protocol provides support for all commands, and register polling. The
ASCII protocol is very similar to the widely used NMEA 0183 protocol supported by most GPS receivers,
and consists of comma delimited parameters printed in human readable text. Below is an example
command request and response on the VN-100 used to poll the attitude (Yaw Pitch Roll Register in the
Attitude subsystem) using the ASCII protocol.
Example Serial Request
$VNRRG,8*4B

Example Serial Response
$VNRRG,08,-114.314,+000.058,-001.773*5F

At the end of this user manual each software subsystem is documented providing a list of all the
commands and registers suported by the subsystem on the VN-100. For each command and register an
example ASCII response is given to demonstrating the ASCII formatting.

3.6.2

Serial Binary

The serial interface offers support for streaming sensor measurements from the sensor at fixed rates using
user configurable binary output packets. These binary output packets provide a low-overhead means of
streaming high-speed sensor measurements from the device minimizing both the required bandwidth and
the necessary overhead required to parse the incoming measurements for the host system.

3.6.3

Serial Command Prompt

A simple command prompt is also provided on the serial interface, which provides support for advanced
device configuration and diagnostics. The serial command prompt is an optional feature that is designed
to provide more detailed diagnostic view of overall system performance than is possible using normal
command & register structure. It is strictly intended to be used by a human operator, who can type
commands to the device using a simple serial terminal, and is not designed to be used programmatically.
Each software subsystem described in the software module chapters provides information on the
diagnostic commands supported by the serial command prompt at the end of each subsystem section.

3.7

System Error Codes

In the event of an error, the VN-100 will output $VNERR, followed by an error code. The possible error
codes are listed in the table below with a description of the error.

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Error Codes

Error Name
Hard Fault

Code
1

Serial Buffer Overflow

Invalid Checksum
Invalid Command
Not Enough Parameters

3
4
5

Too Many Parameters
Invalid Parameter

6
7

Invalid Register
Unauthorized Access
Watchdog Reset

8
9
10

Output Buffer Overflow

Insufficient Baud Rate

Error Buffer Overflow

255

Description
If this error occurs, then the firmware on the VN-100 has experienced a
hard fault exception. To recover from this error the processor will force
a restart, and a discontinuity will occur in the serial output. The
processor will restart within 50 ms of a hard fault error.
The processor’s serial input buffer has experienced an overflow. The
processor has a 256 character input buffer.
The checksum for the received command was invalid.
The user has requested an invalid command.
The user did not supply the minimum number of required parameters
for the requested command.
The user supplied too many parameters for the requested command.
The user supplied a parameter for the requested command which was
invalid.
An invalid register was specified.
The user does not have permission to write to this register.
A watchdog reset has occurred. In the event of a non-recoverable error
the internal watchdog will reset the processor within 50 ms of the error.
The output buffer has experienced an overflow. The processor has a
2048 character output buffer.
The baud rate is not high enough to support the requested
asynchronous data output at the requested data rate.
An overflow event has occurred on the system error buffer.

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3.8

Checksum / CRC

The serial interface provides the option for either an 8-bit checksum or a 16-bit CRC. In the event neither
the checksum nor the CRC is needed, both can be turned off by the user. Refer to the Communication
Protocol Control Register for details on disabling the checksum/CRC.

3.8.1

Checksum Bypass

When communicating with the sensor using a serial terminal, the checksum calculation can be bypassed
by replacing the hexadecimal digits in the checksum with uppercase X characters. This works for both the
8-bit and 16-bit checksum. An example command to read register 1 is shown below using the checksum
bypass feature.
$VNRRG,1*XX

3.8.2

8-bit Checksum

The 8-bit checksum is an XOR of all bytes between, but not including, the dollar sign ($) and asterisk (*).
All comma delimiters are included in the checksum calculation. The resultant checksum is an 8-bit number
and is represented in the command as two hexadecimal characters. The C function snippet below
calculates the correct checksum.
Example C Code
// Calculates the 8-bit checksum for the given byte sequence.
unsigned char calculateChecksum(unsigned char data[], unsigned int length)
{
unsigned int i;
unsigned char cksum = 0;
for(i=0; i> 8) | (crc << 8);
data[i];
(unsigned char)(crc & 0xff) >> 4;
crc << 12;
(crc & 0x00ff) << 5;

return crc;
}

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User Configurable Binary Output Messages

The VN-100 supports 3 separate user configurable binary output messages available on the serial
interface. Each message can be configured by the user to contain any of the available output
measurement types from the IMU, NavState, or NavFilter subsystems. The device can be configured to
asynchronously output each message at a fixed rate based upon a divisor of the IMU internal sampling
rate (IMU Rate).

4.1

Available Output Types

All real-time measurements either measured or estimated by the VN-100 are available using the user
output messages. The different output types are organized into 6 separate output groups. The first group
is a combination of the most common outputs from the remaining groups. The other groups are shown
below.
Binary Outputs
Time
•TimeStartup
•TimeGps
•GpsTow
•GpsWeek
•TimeSyncIn
•TimeGpsPps
•TimeUTC
•SyncInCnt
•SyncOutCnt
•TimeStatus

4.2

IMU
•Status
•UncompMag
•UncompAccel
•UncompAngularRate
•Temp
•Pres
•DeltaTheta
•DeltaVel
•Mag
•Accel
•AngularRate
•SatFlags

Attitude
•Status
•YawPitchRoll
•Quaternion
•DCM
•MagNed
•AccelNed
•LinearAccelBody
•LinearAccelNed
•YprU

Configuring the Output Types

Configuration of the 3 output messages is performed using the User Output Configuration Registers
(Register 75-77). There are 3 separate configuration registers, one for each available output message.
The Binary Output Register 1-3 in the System subsystem section describes in more detail the format for
these registers. In each of these configuration registers the user can select which output types they want
the message to include by specifying the OutputGroup and the OutputFields parameters.

4.2.1

OutputGroup

The OutputGroup and OutputFields parameters consist of variable length arguments to allow conciseness
where possible and expandability where necessary.
The OutputGroup parameter consists of one or more bytes which are used to identify the Binary Output
Groups from which data will be selected for output (see OutputField parameter). Each 8-bit byte consists
of seven group selection bits (Bit 0 through Bit 6) and an extension bit (Bit 7). The extension bit in each
byte is used to indicate the presence of a following continuation byte to select additional (highernumbered) groups. The first byte selects Groups 1-7 (with bit offsets 0-6, respectively), the second byte

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(if present) selects Groups 8-14, and so on. The sequence of group selection bytes will always end with a
byte whose extension bit is not set.
Name
Output Group 1
Output Group 2
Output Group 3
Output Group 5

Bit Offset
0
1
2
4

Description
Common Group
Time Group
IMU Group
Attitude Group

Output group 4, 6, & 7 are not used on the VN-100. The bits for these unused output groups must be
set to zero.

Groups 8-14 are not used, however they are reserved for use in future firmware versions.

4.2.2

OutputFields

The OutputField parameter consists of a series of one or more 16-bit words per selected output group
(see OutputGroup parameter) which are used to identify the selected output fields for that group. The
first series of one or more words corresponds to the fields for the first selected group, followed by a series
of word(s) for the next selected group, and so on. Each 16-bit word consists of 15 group selection bits (Bit
0 through Bit 14) and an extension bit (Bit 15). The extension bit in each word is used to indicate the
presence of a following continuation word to select additional (higher-numbered) output fields for the
current group. The first word corresponding to a specific group selects fields 1-15 (with bit offsets 0-14,
respectively), the second word (if present) selects fields 16-30, and so on. Each sequence of field selection
words corresponding to a selected output group ends with a word whose extension bit is not set, and is
then followed by a sequence of words for the next selected group (if any).
Below is a list of the available output fields for each output group.
Bit
Offset
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Group 1
Common
TimeStartup
Reserved
TimeSyncIn
YawPitchRoll
Quaternion
AngularRate
Reserved
Reserved
Accel
Imu
MagPres
DeltaTheta
VpeStatus
SyncInCnt

Group 2
Time
TimeStartup

TimeSyncIn

SyncInCnt
SyncOutCnt
TimeStatus

Group 3
IMU
ImuStatus
UncompMag
UncompAccel
UncompGyro
Temp
Pres
DeltaTheta
DeltaVel
Mag
Accel
Gyro

Group 5
Attitude
VpeStatus
YawPitchRoll
Quaternion
DCM
MagNed
AccelNed
LinearAccelBody
LinearAccelNed
YprU

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4.2.3

Setup the Configuration Register

Once you have determined the desired outputs for your output messages, you will need to configure the
User Output Message Configuration Registers (Register 75 – 77). These registers are described in detail
under the Binary Output Register 1-3 in the System subsystem section, however for reference the format
of the register is shown below.
Binary Output Register 1-3
75-77
Access : Read / Write
These registers allow the user to construct a custom output message that contains a
Comment :
collection of desired estimated states and sensor measurements.
Size (Bytes): 6-22
Example Response: $VNWRG,75,2,4,1,8*XX
Offset
Name
Format
Unit
Description
0
AsyncMode
uint16
Selects whether the output message should be sent out on
the serial port(s) at a fixed rate.
0 = None. User message is not automatically sent out
either serial port.
1 = Message is sent out serial port 1 at a fixed rate.
2 = Message is sent out serial port 2 at a fixed rate.
3 = Message is sent out both serial ports at a fixed rate.
2
RateDivisor
uint16
Sets the fixed rate at which the message is sent out the
selected serial port(s). The number given is a divisor of the
ImuRate which is nominally 800Hz. For example to have
the sensor output at 50Hz you would set the Divisor equal
to 16.
4+N
OutputGroup(N)
uint8
Selects which output groups are active in the message.
The number of OutputFields in this message should equal
the number of active bits in the OutputGroup.
4+N+2*M OutputField(1)
uint16
Selects which output data fields are active within the
selected output groups.
Register ID :

In the offset column above the variable N is the number of output group bytes. If data is requested
from only groups 1-7, there will be only one output group present (N=1). If data is requested from an
output group of 9-14, then two output groups bytes will be present.
The number of OutputFields present must be equal to the number of output groups selected in the
OutputGroup byte(s). For example if groups 1 and 3 are selected (OutputGroup = 0x05 or 0b00000101),
then there must be two OutputField parameters present (M = 2).

If the number of OutputFields is inconsistent with the number of OutputGroups selected, then the unit
will respond with an invalid parameter error when attempting to write to this register.
If the user attempts to turn on more data than it is possible to send out at the current baud rate, the
unit will resond with a insufficient baud rate error.

To turn off the binary output it is recommended to set the AsyncMode = 0.

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4.2.4

Example Case 1 – Selecting outputs from only the Common Group

For many applications you might be able to get by with only the output types available in the common
group. For these situations the configuration of the output message is simple. Suppose only the following
information shown below is desired.
Bit
Offset
0
3
5

Group 1
Common
TimeStartup
YawPitchRoll
AngularRate

For this example we will assume that the data will be polled using serial port 2 at 50 Hz.
To configure this output message you would send the following command to the VN-100.
$VNWRG,75,2,16,01,0029*XX
Now let’s dissect this command to see what is actually being set:
Field
Header
Command
Register ID
AsyncMode
RateDivisor

Value
$VN
WRG
75
2
16

OutputGroup
GroupField 1

01
0029

Checksum

End Line

\r\n

4.2.5

Description
ASCII message header
Write register command
Register 75 (Config register for first output message)
Message set to output on serial port 2.
Divisor = 16. If the ImuRate = 800Hz then, the message output rate
will be (800 / 16 = 50 Hz).
Groups = 0x01. (Binary group 1 enabled)
Group 1 Field = 0x0029. In binary 0x0029 = 0b00101001.
The active bits correspond to the following active output fields:
Bit 0 – TimeStartup
Bit 3 – YawPitchRoll
Bit 5 - AngularRate
Payload terminator and checksum. XX instructs the VN-100 to
bypass the checksum evaluation. This allows us to manually type
messages in a serial terminal without needing to calculate a valid
checksum.
Carriage return and line feed. Terminates the ASCII message.

Example Case 2 – Outputs from multiple Output Groups without
extention bits

This example case demonstrates how to select multiple output fields from more than one output group.
Assume that the following bold output types are desired:
Bit
Offset
0
1
2
3

Group 1
Common
TimeStartup

Group 3
IMU

Group 5
Attitude

UncompAccel
UncompAngularRate

Quaternion

UM001

MagNed

Also assume that you want the message to stream at 50 Hz over serial port 1.
To configure this output message you would send the following command to the VN-100.
$VNWRG,75,1,16,15,0001,000C,0014*XX
Now let’s dissect this command to see what is actually being set:
Field
Header
Command
Register ID
AsyncMode
RateDivisor

Value
$VN
WRG
75
1
16

OutputGroup

GroupField 1

0001

GroupField 2

000C

GroupField 3

0014

Checksum

End Line

\r\n

UM001

Description
ASCII message header
Write register command
Register 75 (Config register for first output message)
Message sent on serial port 1.
Divisor = 16. If the ImuRate = 800Hz then, the message output rate
will be (800 / 16 = 50 Hz).
Groups = 0x15. In binary 0x15 = 0x00010101.
The active bits correspond to the following active output groups:
Bit 0 – Common
Bit 2 – Imu
Bit 4 - Attitude
Group 1 Field = 0x0001. In binary 0x0001 = 0b00000001.
The active bits correspond to the following active output fields:
Bit 0 – TimeStartup
Group 2 Field = 0x000C. In binary 0x000C = 0b00001100.
The active bits correspond to the following active output fields:
Bit 2 – UncompAccel
Bit 3 – UncompGyro
Group 3 Field = 0x0014. In binary 0x0014 = 0b00010100.
The active bits correspond to the following active output fields:
Bit 2 – Qtn
Bit 4 – MagNed
Payload terminator and checksum. XX instructs the VN-200 to
bypass the checksum evaluation. This allows us to manually type
messages in a serial terminal without needing to calculate a valid
checksum.
Carriage return and line feed. Terminates the ASCII message.

4.3

Serial Output Message Format

The binary output message packets on the serial interface consist of a simple message header, payload,
and a 16-bit CRC. An example packet is shown below for reference. The header is variable length
depending upon the number of groups active in the message.
Header
Field
Byte Offset
Type

4.3.1

Sync

Groups

Group Field 1
2

u16

Payload
Group Field 2
4

u16

CRC

Payload
6

…

CRC
N

N+1

Variable

N+2

u16

Sync Byte

The sync byte is the first byte in the header. Its value will always be equal to 0xFA.

4.3.2

Groups

The Group and Group Field parameters consist of variable length arguments to allow conciseness where
possible and expandability where necessary.
The Group parameter consists of one or more bytes which are used to identify the Binary Output Groups
from which data will be selected for output (see OutputField parameter). Each 8-bit byte consists of seven
group selection bits (Bit 0 through Bit 6) and an extension bit (Bit 7). The extension bit in each byte is used
to indicate the presence of a following continuation byte to select additional (higher-numbered) groups.
The first byte selects Groups 1-7 (with bit offsets 0-6, respectively), the second byte (if present) selects
Groups 8-14, and so on. The sequence of group selection bytes will always end with a byte whose
extension bit is not set. The various groups are shown below.
Name
Binary Group 1
Binary Group 2
Binary Group 3
Binary Group 4
Binary Group 5
Binary Group 6
Binary Group 7
Binary Group 8

Bit Offset
0
1
2
3
4
5
6
7

Description
General Purpose Group.
Time and Event Count Group.
Inertial Measurement Unit Group.
Not used. Must be set to zero.
AHRS Group.
Not used. Must be set to zero.
Not used. Must be set to zero.
Not used. Must be set to zero.

Groups 8-14 are not used, however they are reserved for use in future firmware versions.

UM001

4.3.3

Group Fields

The Group Field parameter consists of a series of one or more 16-bit words per selected output group
which are used to identify the selected output fields for that group. The first series of one or more words
corresponds to the fields for the first selected group, followed by a series of word(s) for the next selected
group, and so on. Each 16-bit word consists of 15 group selection bits (Bit 0 through Bit 14) and an
extension bit (Bit 15). The extension bit in each word is used to indicate the presence of a following
continuation word to select additional (higher-numbered) output fields for the current group. The first
word corresponding to a specific group selects fields 1-15 (with bit offsets 0-14, respectively), the second
word (if present) selects fields 16-30, and so on. Each sequence of field selection words corresponding to
a selected output group ends with a word whose extension bit is not set, and is then followed by a
sequence of words for the next selected group (if any).
The group fields represent which output types have been selected in the active binary groups. The
number of group fields in the header will depend upon how many groups are active in the message. The
number of group fields present in the header will always be equal to the number of active bits in the group
byte. When parsing the binary packet you can count the number of active bits present in the group byte,
and then you can assume that this number of group fields will be present in the header. For example if
only binary group 1 is selected (Group Byte = 0x01), then only one Group field will be present in the
header, thus the header will be 4 bytes in length. If both binary group 1 and 3 are active (Group Byte =
0x05), then two Group field elements will be present in the header (4 bytes), thus the header in this case
will be 6 bytes in length.

4.3.4

Payload

The payload will consist of the output data selected based upon the bits selected in the group byte and
the group field bytes. All output data in the payload section consist of the active outputs selected for
binary group 1, followed by the active outputs selected for binary group 2, and so forth. No padding bytes
are used between output fields.

4.3.5

CRC

The CRC consists of a 16-bit CRC of the packet. The CRC is calculated over the packet starting just after
the sync byte in the header (not including the sync byte) and ending at the end of the payload. More
information about the CRC algorithm and example code for how to perform the calculation is shown in
the Checksum/CRC section of the Software Architecture chapter. The CRC is selected such that if you
compute the 16-bit CRC starting with the group byte and include the CRC itself, a valid packet will result
in 0x0000 computed by the running CRC calculation over the entire packet. This provides a simple way of
detecting packet corruption by simply checking to see if the CRC calculation of the entire packet (not
including the sync byte) results in zero.

UM001

4.3.6

Payload Length

When parsing the packet you will need to know the length of the payload (in bytes) in order to know
where the packet ends in the data stream. In order to reduce the overhead of the packet header length,
the length of the payload is not included in the header. Instead it should be derived based upon
determining the type of data present in the packet. All output data types are fixed length, thus the total
length of the payload can be determined based upon inspection of the group byte and the group field
bytes. In most applications you will likely only use a few binary output types, thus hard coding the payload
length in your parser is the easiest approach. If you want to develop a more generic parser that can handle
all available data output types supported by the VN-100, the easiest approach is to use a table lookup.
Below is a table with the payload size (in bytes) for all available output types.
Binary Output Payload Length In Bytes

Field 1
Field 2
Field 3
Field 4
Field 5
Field 6
Field 7
Field 8
Field 9
Field 10
Field 11
Field 12
Field 13
Field 14
Field 15
Field 16

Group
1

Group
2

Group
3

Group 4

Group
5

Group
6

Group 7

8
8
8
12
16
12
24
12
12
24
20
28
2
4
8
0

8
8
8
2
8
8
8
4
4
1
1
0
0
0
0
0

2
12
12
12
4
4
16
12
12
12
12
2
40
0
0
0

8
8
2
1
1
24
24
12
12
12
4
4
2
28
2+(N*8)
12+(N*28)

2
12
16
36
12
12
12
12
12
12
28
24
0
0
0
0

2
24
24
12
12
12
12
12
12
4
4
68
64
0
0
0

8
8
2
1
1
24
24
12
12
12
4
4
2
28
2+(N*8)
12+(N*28)

The messages highlighted in red in the above table are variable length messages. The size of these
messages will be dependent upon the number of packets present. See the description of the fields in
the appropriate group section below for more information on how to determine the length of these
packets.

The above lookup table can be implemented in C as shown below using a simple 2D array. Assuming you
are only using group 1 through 7, with support for 16 fields per group, then this lookup table could be
implimented using an 8x16 array of bytes consuming only 128 bytes of memory. With the exception of
the SatInfo and RawMeas fields in the GPS group, all other fields have a fixed length. The two variable
length fields can be handled seperately with a case statement. For these two fields the lookup table
contains the length of the fixed portion of the variable length packet (2 for the SatInfo and 12 for the
RawMeas fields).

UM001

Example Code
// 2D array to determine the payload length for a binary output packet. The first
// index of the array is the group number, and the second index
// is the group field index. Both indices are assumed to be zero based.

const unsigned char groupLen[7][16] =
{
{8,

12, 16, 12, 24, 12, 12, 24, 20, 28, 2,

0},

//Group 1

{8,

0},

//Group 2

{2,

12, 12, 12, 4,

16, 12, 12, 12, 12, 2,

40, 0,

0},

//Group 3

{8,

24, 24, 12, 12, 12, 4,

28,

12}, //Group 4

{2,

12, 16, 36, 12, 12, 12, 12, 12, 12, 28, 24, 0,

0},

//Group 5

{2,

24, 24, 12, 12, 12, 12, 12, 12, 4,

68, 64, 0,

0},

//Group 6

{8,

12}, //Group 7

24, 24, 12, 12, 12, 4,

28,

};

4.3.7

Example Cases

To help you better understand how the binary protocol works, the next two sections provide an overview
of how the binary output packets are formed for two separate example cases.

Example Case 1
For example 1 we will assume that only binary group 1 is active, and only the yaw, pitch, and roll output
is active within this binary group. In this case the header will have the following form.
Header
Field
Byte Offset
Byte Value
(Hex)
Type
Value

UM001

Sync

Group

0
FA

1
01

Group 1
Fields
2
3
08 00

u8
0xFA

u8
1

u16
8

4
93

5
50

6
2E

7
42

float
0x422E5093
+43.578686 (Yaw)

8
83

Payload

CRC

YawPitchRoll

CRC

9
3E

10
F1

11
3F

float
0x3FF13E83
+1.8847202 (Pitch)

12
48

13
B5

14
04

15
BB

float
0xBB04B548
-2.0249654e-3 (Roll)

16
92

17
88

u16
0x9288

Example Case 2
For the second example case we will assume that both binary group 1 and 3 are active. In binary group 1,
the Ypr output is selected, and in binary group 3, the Temp output is selected.
Header
Field
Byte Offset
Byte Value
(Hex)
Type
Value

Sync

Group
1
05

Group 1
Fields
2
3
08 00

Group 3
Fields
4
5
01 00

0
FA
u8
0xFA

u8
0x05

u16
0x08

u16
0x01

Payload
Field
Byte Offset
Byte Value
(Hex)
Type
Value

6
A4

7
15

8
02

9
42

float
0x420215A4
+32.521133 (Yaw)

YawPitchRoll
10 11 12 13
4D DF EB 3F
float
0X3FEBDF4D
+1.8427521 (Pitch)

14
F6

CRC
15
1A

16
36

17
BE

float
0XBE361AF6
-1.7783722e-1 (Roll)

18
BF

Temp
19 20
2D A4

21
41

float
0X41A42DBF
+20.522337 (Temp)

CRC
22 23
A8 3A
u16
0XA83A

UM001

4.4

Binary Group 1 – Common Outputs

Binary group 1 contains a wide assortment of commonly used data required for most applications. All of
the outputs found in group 1 are also present in the other groups. In this sense, group 1 is a subset of
commonly used outputs from the other groups. This simplifies the configuration of binary output
messages for applications that only require access to the commonly used data found in group 1. For these
applications you can hard code the group field to 1, and not worry about implemented support for the
other binary groups. Using group 1 for commonly used outputs also has the advantage of reducing the
overall packet size, since the packet length is dependent upon the number of binary groups active.
Binary Group 1

4.4.1

Name
TimeStartup
Reserved
TimeSyncIn
Ypr
Qtn
AngularRate
Reserved
Reserved
Accel
Imu

Bit Offset
0
1
2
3
4
5
6
7
8
9

MagPres

DeltaTheta
InsStatus
SyncInCnt
Reserved
Resv

11
12
13
14
15

Description
Time since startup.
Reserved. Not used on this product.
Time since last SyncIn trigger.
Estimated attitude as yaw pitch and roll angles.
Estimated attitude as a quaternion.
Compensated angular rate.
Reserved. Not used on this product.
Reserved. Not used on this product.
Estimated acceleration (compensated). (Body)
Calibrated uncompensated gyro and accelerometer
measurements.
Calibrated magnetic (compensated), temperature,
and pressure measurements.
Delta time, theta, and velocity.
INS status.
SyncIn count.
Reserved. Not used on this product.
Reserved for future use. Should be set to zero.

Time Startup

The system time since startup measured in nano seconds. The time since startup is based upon the
internal TXCO oscillator for the MCU. The accuracy of the internal TXCO is +/- 20ppm (-40C to 85C). This
field is equivalent to the TimeStartup field in group 2.
TimeStartup
Byte Offset
Type

4.4.2

uint64

TimeSyncIn

The time since the last SyncIn trigger event expressed in nano seconds. This field is equivalent to the
TimeSyncIn field in group 2.
TimeSyncIn
Byte Offset
Type

UM001

uint64

4.4.3

YawPitchRoll

The estimated attitude Yaw, Pitch, and Roll angles measured in degrees. The attitude is given as a 3,2,1
Euler angle sequence describing the body frame with respect to the local North East Down (NED) frame.
This field is equivalent to the YawPitchRoll field in group 5.
YawPitchRoll
pitch

yaw
0

Byte Offset
Type

4.4.4

float

roll
8

float

Quaternion

The estimated attitude quaternion. The last term is the scalar value. The attitude is given as the body
frame with respect to the local North East Down (NED) frame. This field is equivalent to the Quaternion
field in group 5.
qtn[0]
Byte Offset
Type

4.4.5

Quaternion
qtn[2]

qtn[1]

float

qtn[3]
11

float

AngularRate

The estimated angular rate measured in rad/s. The angular rates are compensated by the onboard filter
bias estimates. The angular rate is expressed in the body frame. This field is equivalent to the AngularRate
field in group 3.
AngularRate
rate[1]

rate[0]
Byte Offset
Type

4.4.6

float

rate[2]
8

float

Accel

The estimated acceleration in the body frame, given in m/s^2. This acceleration includes gravity and has
been bias compensated by the onboard INS Kalman filter. This field is equivalent to the Accel field in
group 3.
Accel
accel[1]

accel[0]
Byte Offset
Type

4.4.7

float

accel[2]
7

float

Imu

The uncompensated IMU acceleration and angular rate measurements. The acceleration is given in
m/s^2, and the angular rate is given in rad/s. These measurements correspond to the calibrated angular

UM001

rate and acceleration measurements straight from the IMU. The measurements have not been corrected
for bias offset by the onboard Kalman filter. These are equivalent to the UncompAccel and UncompGyro
fields in group 3.
accel[0]
Byte
Offset
Type

4.4.8

accel[1]
3

float

Imu
rate[0]

accel[2]
7

float

rate[1]
15

float

rate[2]
19

float

MagPres

The compensated magnetic, temperature, and pressure measurements from the IMU. The magnetic
measurement is given in Gauss, and has been corrected for hard/soft iron corrections (if enabled). The
temperature measurement is given in Celsius. The pressure measurement is given in kPa. This field is
equivalent to the Mag, Temp, and Pres fields in group 3.
mag[0]
Byte Offset
Type

4.4.9

MagPres
mag[2]

mag[1]
3

float

temp
12

float

pres

float

DeltaThetaVel

The delta time, angle, and velocity measurements. The delta time (dtime) is the time interval that the
delta angle and velocities are integrated over. The delta theta (dtheta) is the delta rotation angles
incurred due to rotation, since the last time the values were outputted by the device. The delta velocity
(dvel) is the delta velocity incurred due to motion, since the last time the values were outputted by the
device. These delta angles and delta velocities are calculated based upon the onboard conning and
sculling integration performed onboard the sensor at the IMU rate (default 800Hz). The integration for
both the delta angles and velocities are reset each time either of the values are either polled or sent out
due to a scheduled asynchronous ASCII or binary output. This field is equivalent to the DeltaTheta and
DeltaVel fields in group 3 with the inclusion of the additional delta time parameter.
DeltaThetaVel
dtheta[0]
dtheta[1]

dtime
Byte Offset
Type

float

UM001

float

dvel[0]
Byte Offset
Type

float

dtheta[2]
11

float

DeltaThetaVel (continued)
dvel[1]
dvel[2]
19

float

4.4.10 SyncInCnt
The number of SyncIn trigger events that have occurred. This field is equivalent to the SyncInCnt field in
group 2.
SyncInCnt
Byte Offset
Type

u32

UM001

4.5

Binary Group 2 – Time Outputs

Binary group 2 provides all timing and event counter related outputs. Some of these outputs (such as the
TimeGps, TimePps, and TimeUtc), require either that the internal GPS to be enabled, or an external GPS
must be present.
Binary Group 2
Name
TimeStartup
Reserved
Reserved
Reserved
TimeSyncIn
Reserved
Reserved
SyncInCnt
SyncOutCnt
TimeStatus
Resv

4.5.1

Bit Offset
0
1
2
3
4
5
6
7
9
10
11-15

Description
Time since startup.
Reserved. Not used on this product.
Reserved. Not used on this product.
Reserved. Not used on this product.
Time since last SyncIn trigger.
Reserved. Not used on this product.
Reserved. Not used on this product.
SyncIn trigger count.
SyncOut trigger count.
Time valid status flags.
Reserved for future use. Should be set to zero.

TimeStartup

4.5.2

uint64

TimeSyncIn

The time since the last SyncIn event trigger expressed in nano seconds.
TimeSyncIn
Byte Offset
Type

4.5.3

uint64

SyncInCnt

The number of SyncIn trigger events that have occurred.
SyncInCnt
Byte Offset
Type

4.5.4

u32

SyncOutCnt

The number of SyncOut trigger events that have occurred.
SyncOutCnt
Byte Offset
Type

UM001

u32

4.6

Binary Group 3 – IMU Outputs

Binary group 3 provides all outputs which are dependent upon the measurements collected from the
onboard IMU, or an external IMU (if enabled).
Binary Group 3
Name
ImuStatus
UncompMag
UncompAccel
UncompGyro
Temp
Pres
DeltaTheta
DeltaV
Mag
Accel
AngularRate
Resv

4.6.1

Bit Offset
0
1
2
3
4
5
6
7
8
9
10
11-15

Description
Reserved for future use.
Uncompensated magnetic measurement.
Uncompensated acceleration measurement.
Uncompensated angular rate measurement.
Temperature measurement.
Pressure measurement.
Delta theta angles.
Delta velocity.
Compensated magnetic measurement.
Compensated acceleration measurement.
Compensated angular rate measurement.
Reserved for future use. Should be set to zero.

ImuStatus

Status is reserved for future use. Not currently used in the current code, as such will always report 0.
ImuStatus
0

Byte Offset
Type

4.6.2

u16

UncompMag

The IMU magnetic field measured in units of Gauss, given in the body frame. This measurement is
compensated by the static calibration (individual factory calibration stored in flash), and the user
compensation, however it is not compensated by the onboard Hard/Soft Iron estimator.
UncompMag
mag[1]

mag[0]
Byte Offset
Type

4.6.3

float

mag[2]
8

float

UncompAccel

The IMU acceleration measured in units of m/s^2, given in the body frame. This measurement is
compensated by the static calibration (individual factory calibration stored in flash), however it is not
compensated by any dynamic calibration such as bias compensation from the onboard INS Kalman filter.
UncompAccel
accel[1]

accel[0]
Byte Offset
Type

float

accel[2]
8

float

UM001

4.6.4

UncompGyro

The IMU angular rate measured in units of rad/s, given in the body frame. This measurement is
compensated by the static calibration (individual factory calibration stored in flash), however it is not
compensated by any dynamic calibration such as the bias compensation from the onboard AHRS/INS
Kalman filters.
UncompGyro
gyro[1]

gyro[0]
0

Byte Offset
Type

4.6.5

float

gyro[2]
8

float

Temp

The IMU temperature measured in units of Celsius.
Temp
0

Byte Offset
Type

4.6.6

float

Pres

The IMU pressure measured in kilopascals. This is an absolute pressure measurement. Typical pressure
at sea level would be around 100 kPa.
Pres
0

Byte Offset
Type

4.6.7

float

DeltaTheta

The delta theta (dtheta) is the delta rotation angles incurred due to rotation, since the last time the values
were output by the device. The delta angles are calculated based upon the onboard conning and sculling
integration performed onboard the sensor at the IMU sampling rate (nominally 800Hz). The delta time
(dtime) is the time interval that the delta angle and velocities are integrated over. The integration for the
delta angles are reset each time the values are either polled or sent out due to a scheduled asynchronous
ASCII or binary output. Time is given in sections. Delta angles are given in degrees.
Fields
Byte Offset
Type

UM001

dtime
0

float

dtheta[0]
3

float

DeltaTheta
dtheta[1]
7

float

dtheta[2]
11

float

4.6.8

DeltaV

The delta velocity (dvel) is the delta velocity incurred due to motion, since the last time the values were
output by the device. The delta velocities are calculated based upon the onboard conning and sculling
integration performed onboard the sensor at the IMU sampling rate (nominally 800Hz). The integration
for the delta velocities are reset each time the values are either polled or sent out due to a scheduled
asynchronous ASCII or binary output. Delta velocity is given in meters per second.
Fields
Byte Offset
Type

4.6.9

DeltaVel
dvel[1]

dvel[0]
0

float

dvel[2]
8

float

Mag

The IMU compensated magnetic field measured units of Gauss, and given in the body frame. This
measurement is compensated by the static calibration (individual factory calibration stored in flash), the
user compensation, and the dynamic calibration from the onboard Hard/Soft Iron estimator.
Mag
mag[1]

mag[0]
Byte Offset
Type

float

mag[2]
7

float

4.6.10 Accel
The compensated acceleration measured in units of m/s^2, and given in the body frame. This
measurement is compensated by the static calibration (individual factory calibration stored in flash), the
user compensation, and the dynamic bias compensation from the onboard INS Kalman filter.
Accel
accel[1]

accel[0]
Byte Offset
Type

float

accel[2]
7

float

4.6.11 AngularRate
The compensated angular rate measured in units of rad/s, and given in the body frame. This measurement
is compensated by the static calibration (individual factor calibration stored in flash), the user
compensation, and the dynamic bias compensation from the onboard INS Kalman filter.
AngularRate
gyro[1]

gyro[0]
Byte Offset
Type

float

gyro[2]
8

float

UM001

4.7

Binary Group 5 – Attitude Outputs

Binary group 5 provides all estimated outputs which are dependent upon the estimated attitude solution.
The attitude will be derived from either the AHRS or the INS, depending upon which filter is currently
active and tracking. All of the fields in this group will only be valid if the AHRS/INS filter is currently enabled
and tracking.
Binary Group 5
Name
VpeStatus
Ypr
Qtn
DCM
MagNed
AccelNed
LinearAccelBody
LinearAccelNed
YprU
Resv

4.7.1

Bit Offset
0
1
2
3
4
5
6
7
8
9-15

Description
VPE Status
Yaw Pitch Roll
Quaternion
Directional Cosine Matrix
Compensated magnetic (NED)
Compensated acceleration (NED)
Compensated linear acceleration (no gravity)
Compensated linear acceleration (no gravity) (NED)
Yaw Pitch Roll uncertainty
Reserved for future use. Should be set to zero.

VpeStatus

The VPE status bitfield.
VpeStatus
Byte Offset
Type

u16

VpeStatus BitField

AttitudeQuality

Bit
Offset
0

GyroSaturation
GyroSaturationRecovery

2
3

1 bit
1 bit

MagDisturbance

2 bit

MagSaturation
AccDisturbance

6
7

1 bit
2 bit

AccSaturation
Reserved

9
10

1 bit
1 bit

KnownMagDisturbance

1 bit

KnownAccelDisturbance

1 bit

Reserved

3 bits

Name

UM001

Format

Unit

Description

2 bits

Provides an indication of the quality of the attitude
solution.
At least one gyro axis is currently saturated.
Filter is in the process of recovering from a gyro
saturation event.
A magnetic DC disturbance has been detected.
0 – No magnetic disturbance
1 to 3 – Magnetic disturbance is present.
At least one magnetometer axis is currently saturated.
A strong acceleration disturbance has been detected.
0 – No acceleration disturbance.
1 to 3 – Acceleration disturbance has been detected.
At least one accelerometer axis is currently saturated.
Reserved for internal use. May change state at runtime.
A known magnetic disturbance has been reported by
the user and the magnetometer is currently tuned out.
A known acceleration disturbance has been reported by
the user and the accelerometer is currently tuned out.
Reserved for future use.

Table 1 - AttitudeQuality Field
Value
0
1
2
3

4.7.2

Description
Excellent
Good
Bad
Not tracking

YawPitchRoll

yaw
0

Byte Offset
Type

4.7.3

float

roll
8

float

Quaternion

The estimated attitude quaternion. The last term is the scalar value. The attitude is given as the body
frame with respect to the local North East Down (NED) frame.
Quaternion
qtn[1]
qtn[2]

qtn[0]
Byte Offset
Type

4.7.4

float

qtn[3]
11

float

DCM

The estimated attitude directional cosine matrix given in column major order. The DCM maps vectors
from the North East Down (NED) frame into the body frame.
Fields
Byte
Offset
Type

dcm[0]
0

dcm[1]
3

float

Fields
Byte Offset
Type

4.7.5

Dcm
dcm[3]

dcm[2]
10

float

dcm[4]
15

float

Dcm (continued)
dcm[7]

dcm[6]
24

dcm[5]
19

float

dcm[8]
32

float

MagNed

The current estimated magnetic field (Gauss), given in the North East Down (NED) frame. The current
attitude solution is used to map the measurement from the measured body frame to the inertial (NED)
frame. This measurement is compensated by both the static calibration (individual factory calibration
50

UM001

stored in flash), and the dynamic calibration such as the user or onboard Hard/Soft Iron compensation
registers.
MagNed
mag[1]

mag[0]
Byte Offset
Type

4.7.6

float

mag[2]
8

float

AccelNed

The estimated acceleration (with gravity) reported in m/s^2, given in the North East Down (NED) frame.
The acceleration measurement has been bias compensated by the onboard INS filter. This measurement
is attitude dependent, since the attitude is used to map the measurement from the body frame into the
inertial (NED) frame. If the device is stationary and the INS filter is tracking, the measurement should be
nominally equivalent to the gravity reference vector in the inertial frame (NED).
AccelNed
accel[1]

accel[0]
Byte Offset
Type

4.7.7

float

accel[2]
8

float

LinearAccelBody

The estimated linear acceleration (without gravity) reported in m/s^2, and given in the body frame. The
acceleration measurement has been bias compensated by the onboard INS filter, and the gravity
component has been removed using the current gravity reference vector model. This measurement is
attitude dependent, since the attitude solution is required to map the gravity reference vector (known in
the inertial NED frame), into the body frame so that it can be removed from the measurement. If the
device is stationary and the onboard INS filter is tracking, the measurement nominally will read 0 in all
three axes.
LinearAccelBody
accel[1]
accel[2]

accel[0]
Byte Offset
Type

UM001

float

4.7.8

LinearAccelNed

The estimated linear acceleration (without gravity) reported in m/s^2, and given in the North East Down
(NED) frame. This measurement is attitude dependent as the attitude solution is used to map the
measurement from the body frame into the inertial (NED) frame. This acceleration measurement has
been bias compensated by the onboard INS filter, and the gravity component has been removed using the
current gravity reference vector estimate. If the device is stationary and the onboard INS filter is tracking,
the measurement nominally will read 0 in all three axes.
LinearAccelNed
accel[1]

accel[0]
Byte Offset
Type

4.7.9

float

accel[2]
9

float

YprU

The estimated attitude (Yaw, Pitch, Roll) uncertainty (1 Sigma), reported in degrees.
YprU
pitch

yaw
Byte Offset
Type

float

roll
7

float

The estimated attitude (YprU) field is not valid when the INS Scenario mode in the INS Basic
Configuration register is set to AHRS mode. See the INS Basic Configuration Register in the INS section
for more details.

UM001

System Module

5.1
5.1.1

Commands
Read Register Command

This command allows the user to read any of the registers on the VN-100. The only required parameter
is the ID of the register to be read. The first parameter of the response will contain the same register ID
followed by a variable number of parameters. The number of parameters and their formatting is specific
to the requested register. Refer to the appropriate register listed in the subsystem sections for details on
this formatting. If an invalid register is requested, an error code will be returned.
Example Read Register Command
Example Command
UART Command
UART Response

5.1.2

Message
$VNRRG,5*46
$VNRRG,5,9600*65

Write Register Command

This command is used to write data values to a specified register on the VN-100 module. The ID of the
register to be written to is the first parameter. This is followed by the data values specific to that register.
Refer to the appropriate register listed in the subsystem sections for details on this formatting. If an
invalid register is requested, an error code will be returned.
Example Write Register Command
Example Command
UART Command
UART Response

UM001

Message
$VNWRG,5,9600*60
$VNWRG,5,9600*60

5.1.3

Write Settings Command

This command will write the current register settings into non-volatile memory. Once the settings are
stored in non-volatile (Flash) memory, the VN-100 module can be power cycled or reset, and the register
will be reloaded from non-volatile memory.
Example Write Settings Command
Example Command
UART Command
UART Response

Message
$VNWNV*57
$VNWNV*57

Due to limitations in the flash write speed the write settings command takes ~ 500ms to complete. Any
commands that are sent to the sensor during this time will be responded to after the operation is
complete.

The sensor must be stationary when issuing a Write Settings Command otherwise a Reset command
must also be issued to prevent the Kalman Filter from diverging during the write settings process.

5.1.4

Restore Factory Settings Command

This command will restore the VN-100 module’s factory default settings and will reset the module. There
are no parameters for this command. The module will respond to this command before restoring the
factory settings.
Example Restore Factory Settings Command
Example Command
UART Command
UART Response

5.1.5

Message
$VNRFS*5F
$VNRFS*5F

Reset Command

This command will reset the module. There are no parameters required for this command. The module
will first respond to the command and will then perform a reset. Upon a reset all registers will be reloaded
with the values saved in non-volatile memory. If no values are stored in non-volatile memory, the device
will default to factory settings. Also upon reset the VN-100 will re-initialize its Kalman filter, thus the filter
will take a few seconds to completely converge on the correct attitude and correct for gyro bias.
Example Reset Command
Example Command
UART Command
UART Response

Message
$VNRST*4D
$VNRST*4D

UM001

5.1.6

Firmware Update Command

This command is used to enter the boot loader for performing firmware updates. Upon receiving this
command on serial port 1, the VN-100 will enter into firmware reprogramming mode. The easiest method
of updating firmware is to use one of the VectorNav Firmware Update Tools. If you wish however to
incorporate the ability to update the firmware into your own system, the protocol and procedure for
updating the firmware is outlined in the AN013 Firmware Update Protocol application note.
Example Firmware Update Command
Example Command
UART Command
UART Response

Message
$VNFWU*XX
$VNFWU*XX

Firmware updates are only supported on serial port 1. If you plan on using either serial port 2 as your
primary means of communicating with the sensor, it is recommended that you also provide support in
your design to communicate with the sensor using serial port 1 to facilitate firmware updates.

5.1.7

Serial Command Prompt Command

This command allows you to enter into the command prompt mode on either serial port. The command
mode supports a wide range of diagnostics and configuration options that go beyond the abilities of the
normal read/write configuration register interface.
Example Command Prompt Command
Example Command
UART Command
UART Response

UM001

Message
$VNCMD*XX
$VNCMD*XX

5.1.8

Asynchronous Output Pause Command

This command allows the user to temporarily pause the asynchronous outputs on the given serial port.
When paused, both the ASCII and the 3 binary asynchronous output messages will temporarily stop
outputting from the device on the serial port for which this command is received. The state of the
asynchronous output register and the binary output configuration registers will not be changed when the
asynchronous outputs are paused. This command is useful when you want to send configuration
commands to the VN-100, but do not want to deal with the additional overhead of having to parse a
constant stream of asynchronous output messages while waiting for the response to your configuration
commands. It is also useful when you want to type commands to the device from a serial command
prompt. The below example commands demonstrate how to pause and resume asynchronous outputs.
Example Asynchronous Pause/Resume Commands
Example Command
Pause Async Outputs
Resume Async Outputs

5.1.9

Message
$VNASY,0*XX
$VNASY,1*XX

Binary Output Poll Command

This command allows you to poll the sensor measurements available in the binary output protocol.
Example Command Prompt Command
Example Command
UART Command

UART Response

Message
$VNBOM,N*XX
Where N is 1-3 to selecte the appropriate binary
output register.
Responds with requested binary packet.

To use the Binary Output Poll command you will first need to configure the desired output packet using
the Binary Output Register 1-3. If you wish only to poll this output, set the rate in the Binary Output
Register to 0. When you wish to poll the measurement send the command $VNBOM,N*XX where the
N is the number of the appropriate binary output register.

UM001

5.2

Configuration Registers

5.2.1

User Tag Register
User Tag
Register ID :
Comment :

Offset
0

Size (Bytes):
Example Response:
Name
Tag

Access :

Read /
Write
User assigned tag register. Any values can be assigned to this register. They
will be stored to flash upon issuing a write settings command.
20
$VNRRG,00,SENSOR_A14*52
Format
Unit Description
char
User defined tag register. Up to 20 bytes or characters. If a
string with more than 20 characters is given, then the string
will be truncated to the first 20.

Only printable ASCII characters are allowed for the user tag register.
Allowable characters include any character in the hexadecimal range of 0x20 to 0x7E, excluding 0x24
(‘$’), 0x2C (‘,’), and 0x2A (‘*’). The use any other character will result in an invalid parameter error code
returned. This restriction is required to ensure that the value set in the user tag register remains
accessible using the serial ASCII protocol.

UM001

5.2.2

Model Number Register

Model Number
1
Model Number
24
$VNRRG,01,VN-310*58
Format
Unit Description
char
Product name. Max 24 characters.

Access :

Read Only

UM001

5.2.3

Hardware Revision Register

UM001

2
Hardware revision.
4
$VNRRG,02,1*6C
Format
uint32

Access :

Unit
-

Read Only

Description
Hardware revision.

5.2.4

Serial Number Register

Serial Number
3
Access :
Serial Number
4
$VNRRG,03,0100011981*5D
Format
Unit Description
uint32
Serial Number (32-bit unsigned integer)

Read Only

UM001

5.2.5

Firmware Version Register

Register ID :
Comment :
Size (Bytes):
Example Response:
Offset Name
0
Major
Version
1
Minor
Version
2
Feature
Version
3
HotFix

UM001

Firmware Version Register
4
Firmware version.
4
$VNRRG,04,0.4.0.0*71
Format
Unit Description
uint8
Major release version of firmware.

Access :

Read Only

uint8

Minor release version of firmware

uint8

Feature release version of the firmware.

uint8

Hot fix number. Numbers above 100 are reserved for
custom firmware versions.

5.2.6

Serial Baud Rate Register
Serial Baud Rate
Register ID :

Offset
0
4

Comment :
Size (Bytes):
Example Command:
Name
Baud Rate
Serial Port

Access :

Read /
Write

Serial baud rate.
4
$VNWRG,05,115200*58
Format
Unit Description
uint32
Serial baud rate.
uint8
Optional. The serial port to change the baud rate on.
If this parameter is not provided then the baud rate will be
changed for the active serial port.
1 – Serial Port 1
2 – Serial Port 2

Baud Rate Settings
Acceptable
Baud Rates
9600
19200
38400
57600
115200
128000
230400
460800
921600

The serial port parameter in this register is optional. If it is not provided, the baud rate will be changed
on the active serial port. The response to this register will include the serial port parameter if the
optional parameter is provided. If the second parameter is not provided then the response will not
include this parameter.

Upon receiving a baud rate change request, the VN-100 will send the response prior to changing the
baud rate.

UM001

5.2.7

Async Data Output Type Register
Asynchronous Data Output Type
Register ID :

Offset
0
4

Comment :
Size (Bytes):
Example Command:
Name
ADOR
Serial Port

Access :

Read /
Write

Asynchronous data output type.
4
$VNWRG,06,0*6C
Format
Unit Description
uint32
Output register.
uint8
Optional. The serial port to change the asynchronous data
type on. If this parameter is not provided then the ADOR
will be changed for the active serial port.
1 – Serial Port 1
2 – Serial Port 2

This register controls the type of data that will be asynchronously outputted by the module. With this
register, the user can specify which data register will be automatically outputted when it gets updated
with a new reading. The table below lists which registers can be set to asynchronously output, the value
to specify which register to output, and the header of the asynchronous data packet. Asynchronous data
output can be disabled by setting this register to zero. The asynchronous data output will be sent out
automatically at a frequency specified by the Async Data Output Frequency Register.
The serial port parameter in this register is optional. If it is not provided, the ADOF will be changed on
the active serial port. The response to this register will include the serial port parameter if the optional
parameter is provided. If the second parameter is not provided, the response will not include this
parameter.

UM001

Asynchronous Solution Output Settings
Setting
0
1
2
8
9
10
11
12
13
14
16
17
19
20
21
22
23
30

Asynchronous Solution Output Type
Asynchronous output turned off
Yaw, Pitch, Roll
Quaternion
Quaternion, Magnetic, Acceleration and Angular Rates
Directional Cosine Orientation Matrix
Magnetic Measurements
Acceleration Measurements
Angular Rate Measurements
Magnetic, Acceleration, and Angular Rate Measurements
Yaw, Pitch, Roll, Magnetic, Acceleration, and Angular Rate
Measurements
Yaw, Pitch, Roll, Body True Acceleration, and Angular Rates
Yaw, Pitch, Roll, Inertial True Acceleration, and Angular
Rates
IMU Measurements
GPS LLA
GPS ECEF
INS LLA
INS ECEF
Delta theta and delta velocity

Header
N/A
VNYPR
VNQTN
VNQMR
VNDCM
VNMAG
VNACC
VNGYR
VNMAR
VNYMR
VNYBA
VNYIA
VNIMU
VNGPS
VNGPE
VNINS
VNINE
VNDTV

UM001

5.2.8

Async Data Output Frequency Register
Asynchronous Data Output Frequency
Register ID :

Offset
0
4

Comment :
Size (Bytes):
Example Command:
Name
ADOF
Serial Port

Access :

Read /
Write

Asynchronous data output frequency.
4
$VNWRG,07,40*59
Format
Unit Description
uint32
Hz
Output frequency.
uint8
Optional. The serial port to change the asynchronous data
type frequency on. If this parameter is not provided then
the ADOF will be changed for the active serial port.
1 – Serial Port 1
2 – Serial Port 2

ADOR Data Rates
Acceptable
Data Rates (Hz)
1
2
4
5
10
20
25
40
50
100
200

The serial port parameter in this register is optional. If it is not provided, the ADOF will be changed on
the active serial port. The response to this register will include the serial port parameter if the optional
parameter is provided. If the second parameter is not provided, the response will not include this
parameter.

UM001

5.2.9

Synchronization Control
Synchronization Control
32
Access : Read / Write
Contains parameters which allow the timing of the VN-100 to be synchronized
with external devices.
20
$VNRRG,32,3,0,0,0,6,1,0,100000000,0*6B
Format
Unit Description
uint8
Input signal synchronization mode
uint8
Input signal synchronization edge selection
uint16
Input signal trigger skip factor
uint32
Reserved for future use. Defaults to 0.
uint8
Output synchronization signal mode
uint8
Output synchronization signal polarity
uint16
Output synchronization signal skip factor
uint32
ns
Output synchronization signal pulse width
uint32
Reserved for future use. Defaults to 0.

Offset
0
1
2
4
8
9
10
12
16

Size (Bytes):
Example Response:
Name
SyncInMode
SyncInEdge
SyncInSkipFactor
RESERVED
SyncOutMode
SyncOutPolarity
SyncOutSkipFactor
SyncOutPulseWidth
RESERVED

SyncInMode
The SyncInMode register controls the behavior of the SyncIn event. If the mode is set to COUNT then the
internal clock will be used to control the IMU sampling. If SyncInMode is set to IMU then the IMU sampling
loop will run on a SyncIn event. The relationship between the SyncIn event and a SyncIn trigger is defined
by the SyncInEdge and SyncInSkipFactor parameters. If set to ASYNC then the VN-100 will output
asynchronous serial messages upon each trigger event.
SyncIn Mode
Mode
COUNT
IMU
ASYNC

Pin
SYNC_IN
SYNC_IN
SYNC_IN

Value
3
4
5

ASYNC3

SYNC_IN

Description
Count number of trigger events on SYNC_IN.
Start IMU sampling on trigger of SYNC_IN.
Output asynchronous message on trigger of SYNC_IN.
Output asynchronous or binary messages configured with a rate of 0 to
output on trigger of SYNC_IN.

In ASYNC3 mode messages configured with an output rate = 0 are output each time the appropriate
transistion edge of the SyncIn pin is captured according to the edge settings in the SyncInEdge field.
Messages configured with output rate > 0 are not affected by the SyncIn puse. This applies to the ASCII
Async message set by the Async Data Output Register, the user configurate binary output messages set
by the Binary Output Registers, as well as the NMEA messages configured by the NMEA Output
Registers.

UM001

SyncInEdge
The SyncInEdge register controls the type of edge the signal is set to trigger on. The factory default state
is to trigger on a rising edge.
SyncInEdge Mode
Value
0
1

Description
Trigger on rising edge
Trigger on falling edge

SyncInSkipFactor
The SyncInSkipFactor defines how many times trigger edges defined by SyncInEdge should occur prior to
triggering a SyncIn event. The action performed on a SyncIn event is determined by the SyncIn mode. As
an example if the SyncInSkipFactor was set to 4 and a 1 kHz signal was attached to the SyncIn pin, then
the SyncIn event would only occur at 200 Hz.

SyncOutMode
The SyncOutMode register controls the behavior of the SyncOut pin. If this is set to IMU then the SyncOut
will start the pulse when the internal IMU sample loop starts. This mode is used to make a sensor the
Master in a multi-sensor network array. If this is set to IMU_READY mode then the pulse will start when
IMU measurements become available. If this is set to INS mode then the pulse will start when attitude
measurements are made available. Changes to this register take effect immediately.
SyncOutMode
Mode
NONE
IMU_START
IMU_READY
INS

Value
0
1
2
3

Description
None
Trigger at start of IMU sampling
Trigger when IMU measurements are available
Trigger when attitude measurements are available

SyncOutPolarity
The SyncOutPolarity register controls the polarity of the output pulse on the SyncOut pin. Changes to this
register take effect immediately.
SyncOutPolarity
Value
0
1

Description
Negative Pulse
Positive Pulse

SyncOutSkipFactor
The SyncOutSkipFactor defines how many times the sync out event should be skipped before actually
triggering the SyncOut pin.

SyncOutPulseWidth
The SyncOutPulseWidth field controls the desired width of the SyncOut pulse. The default value is
100,000,000 (100 ms).
UM001

5.2.10 Communication Protocol Control
Communication Protocol Control
Read /
Write
Comment : Contains parameters that controls the communication protocol used by the sensor.
Size (Bytes): 7
Example Response: $VNRRG,30,0,0,0,0,1,0,1*6C
Offset Name
Format Unit
Description
Provides the ability to append a counter or time to the end
0
SerialCount
uint8
of the serial asynchronous messages.
Provides the ability to append the status to the end of the
1
SerialStatus
uint8
serial asynchronous messages.
Provides the ability to append a counter to the end of the
2
SPICount
uint8
SPI packets.
Provides the ability to append the status to the end of the
3
SPIStatus
uint8
SPI packets.
Choose the type of checksum used for serial
4
SerialChecksum
uint8
communications.
Choose the type of checksum used for the SPI
5
SPIChecksum
uint8
communications.
6
ErrorMode
uint8
Choose the action taken when errors are generated.
Register ID :

Access :

UM001

Serial Count
The SerialCount field provides a means of appending a time or counter to the end of all asynchronous
communication messages transmitted on the serial interface. The values for each of these counters come
directly from the Synchronization Status Register in the System subsystem.
With the SerialCount field set to OFF a typical serial asynchronous message would appear as the following:
$VNYPR,+010.071,+000.278,-002.026*60

With the SerialCount field set to one of the non-zero values the same asynchronous message would
appear instead as:
$VNYPR,+010.071,+000.278,-002.026,T1162704*2F

When the SerialCount field is enabled the counter will always be appended to the end of the message just
prior to the checksum. The counter will be preceded by the T character to distinguish it from the status
field.
SerialCount Field
Mode
NONE
SYNCIN_COUNT
SYNCIN_TIME
SYNCOUT_COUNT
GPS_PPS

Value
0
1
2
3
4

Description
OFF
SyncIn Counter
SyncIn Time
SyncOut Counter
Gps Pps Time

SerialStatus
The SerialStatus field provides a means of tracking real-time status information pertaining to the overall
state of the sensor measurements and onboard filtering algorithm. As with the SerialCount, a typical serial
asynchronous message would appear as the following:
$VNYPR,+010.071,+000.278,-002.026*60

With the SerialStatus field set to one of the non-zero values, the same asynchronous message would
appear instead as:
$VNYPR,+010.071,+000.278,-002.026,S0000*1F

When the SerialStatus field is enabled the status will always be appended to the end of the message just
prior to the checksum. If both the SerialCount and SerialStatus are enabled then the SerialStatus will be
displayed first. The counter will be preceded by the S character to distinguish it from the counter field.
The status consists of 4 hexadecimal characters.
SerialStatus
Value
0
1
2

UM001

Description
OFF
VPE Status
INS Status

SPICount
The SPICount field provides a means of appending a time or counter to the end of all SPI packets. The
values for each of these counters come directly from the Synchronization Status Register.
SPICount Field
Mode
NONE
SYNCIN_COUNT
SYNCIN_TIME
SYNCOUT_COUNT
GPS_PPS

Value
0
1
2
3
4

Description
OFF
SyncIn Counter
SyncIn Time
SyncOut Counter
Gps Pps Time

SPIStatus
The AsyncStatus field provides a means of tracking real-time status information pertaining to the overall
state of the sensor measurements and onboard filtering algorithm. This information is very useful in
situations where action must be taken when certain crucial events happen such as the detection of gyro
saturation or magnetic interference.
SPIStatus
Value
0
1
2

Description
OFF
VPE Status
INS Status

SerialChecksum
This field controls the type of checksum used for the serial communications. Normally the VN-100 uses
an 8-bit checksum identical to the type used for normal GPS NMEA packets. This form of checksum
however offers only a limited means of error checking. As an alternative a full 16-bit CRC (CRC16-CCITT
with polynomial = 0x07) is also offered. The 2-byte CRC value is printed using 4 hexadecimal digits.
SerialChecksum
Value
1
3

Description
8-Bit Checksum
16-Bit CRC

SPIChecksum
This field controls the type of checksum used for the SPI communications. The checksum is appended to
the end of the binary data packet. The 16-bit CRC is identical to the one described above for the
SerialChecksum.
SPIChecksum
Value
0
1
3

Description
OFF
8-Bit Checksum
16-Bit CRC

UM001

ErrorMode
This field controls the type of action taken by the VN-100 when an error event occurs. If the send error
mode is enabled then a message similar to the one shown below will be sent on the serial bus when an
error event occurs.
$VNERR,03*72

Regardless of the state of the ErrorMode, the number of error events is always recorded and is made
available in the SysErrors field of the Communication Protocol Status Register in the System subsystem.
ErrorMode
Value
0
1
2

Description
Ignore Error
Send Error
Send Error and set ADOR register to OFF

Example Async Messages
The following table shows example asynchronous messages with the AsyncCount and the AsyncStatus
values appended to the end.
Example Type
Async Message with
AsyncCount Enabled
Async Message with
AsyncStatus Enabled
Async Message with
AsyncCount and
AsyncStatus Enabled

UM001

Message
$VNYPR,+010.071,+000.278,-002.026,T1162704*2F
$VNYPR,+010.071,+000.278,-002.026,S0000*1F
$VNYPR,+010.071,+000.278,-002.026,T1162704,S0000*50

5.2.11 Binary Output Register 1
Binary Output Register 1
75
Access : Read / Write
This register allows the user to construct a custom binary output message that contains a
Comment :
collection of desired estimated states and sensor measurements.
Size (Bytes): 6-22
Example Response: $VNWRG,75,2,4,1,8*XX
Offset
Name
Format
Unit Description
0
AsyncMode
uint16
Selects whether the output message should be sent out on the
serial port(s) at a fixed rate.
0 = None. User message is not automatically sent out either
serial port.
1 = Message is sent out serial port 1 at a fixed rate.
2 = Message is sent out serial port 2 at a fixed rate.
3 = Message is sent out both serial ports at a fixed rate.
2
RateDivisor
uint16
Sets the fixed rate at which the message is sent out the
selected serial port(s). The number given is a divisor of the
ImuRate which is nominally 800Hz. For example to have the
sensor output at 50Hz you would set the Divisor equal to 16.
4
OutputGroup
uint16
Selects which output groups are active in the message. The
number of OutputFields in this message should equal the
number of active bits in the OutputGroup.
4+N
OutputGroup(N) uint8
Selects which output groups are active in the message. The
number of OutputFields in this message should equal the
number of active bits in the OutputGroup.
4+N+2*M OutputField(1)
uint16
Selects which output data fields are active within the selected
output groups.
Register ID :

See the User Configurable Binary Output Messages section for information on the format for the Groups
and Group Fields.
In the offset column above the variable N is the number of output group bytes. If data is requested
from only groups 1-7, there will be only one output group present (N=1). If data is requested from an
output group of 9-14, then two output groups bytes will be present.
The number of OutputFields present must be equal to the number of output groups selected in the
OutputGroup byte(s). For example if groups 1 and 3 are selected (OutputGroup = 0x05 or 0b00000101),
then there must be two OutputField parameters present (M = 2).

To turn off the binary output it is recommended to set the AsyncMode = 0.

UM001

5.2.12 Binary Output Register 2
Binary Output Register 2
76
Access : Read / Write
This register allows the user to construct a custom binary output message that contains a
Comment :
collection of desired estimated states and sensor measurements.
Size (Bytes): 6-22
Example Response: $VNWRG,76,2,4,1,8*XX
Offset
Name
Format
Unit Description
0
AsyncMode
uint16
Selects whether the output message should be sent out on the
serial port(s) at a fixed rate.
0 = None. User message is not automatically sent out either
serial port.
1 = Message is sent out serial port 1 at a fixed rate.
2 = Message is sent out serial port 2 at a fixed rate.
3 = Message is sent out both serial ports at a fixed rate.
2
RateDivisor
uint16
Sets the fixed rate at which the message is sent out the
selected serial port(s). The number given is a divisor of the
ImuRate which is nominally 800Hz. For example to have the
sensor output at 50Hz you would set the Divisor equal to 16.
4
OutputGroup
uint16
Selects which output groups are active in the message. The
number of OutputFields in this message should equal the
number of active bits in the OutputGroup.
4+N
OutputGroup(N) uint8
Selects which output groups are active in the message. The
number of OutputFields in this message should equal the
number of active bits in the OutputGroup.
4+N+2*M OutputField(1)
uint16
Selects which output data fields are active within the selected
output groups.
Register ID :

To turn off the binary output it is recommended to set the AsyncMode = 0.

UM001

5.2.13 Binary Output Register 3
Binary Output Register 3
77
Access : Read / Write
This register allows the user to construct a custom binary output message that contains a
Comment :
collection of desired estimated states and sensor measurements.
Size (Bytes): 6-22
Example Response: $VNWRG,77,2,4,1,8*XX
Offset
Name
Format
Unit Description
0
AsyncMode
uint16
Selects whether the output message should be sent out on the
serial port(s) at a fixed rate.
0 = None. User message is not automatically sent out either
serial port.
1 = Message is sent out serial port 1 at a fixed rate.
2 = Message is sent out serial port 2 at a fixed rate.
3 = Message is sent out both serial ports at a fixed rate.
2
RateDivisor
uint16
Sets the fixed rate at which the message is sent out the
selected serial port(s). The number given is a divisor of the
ImuRate which is nominally 800Hz. For example to have the
sensor output at 50Hz you would set the Divisor equal to 16.
4
OutputGroup
uint16
Selects which output groups are active in the message. The
number of OutputFields in this message should equal the
number of active bits in the OutputGroup.
4+N
OutputGroup(N) uint8
Selects which output groups are active in the message. The
number of OutputFields in this message should equal the
number of active bits in the OutputGroup.
4+N+2*M OutputField(1)
uint16
Selects which output data fields are active within the selected
output groups.
Register ID :

To turn off the binary output it is recommended to set the AsyncMode = 0.

UM001

5.3

Status Registers

5.3.1

Synchronization Status

Synchronization Status
33
Access : Read / Write
Contains status parameters that pertaining to the communication synchronization features.
12
$VNRRG,33,2552498,0,0*6A

Offset

Name

Format

Unit

SyncInCount

uint32

SyncInTime

uint32

µs

SyncOutCount

uint32

Description
Keeps track of the number of times that the SyncIn
trigger even has occured. This register can be used to
correlate the attitude to an event on an external
system such as a camera or GPS.
It is also possible to have the value of this register
appended to each asynchronous data packet on the
serial bus. This can be done by setting the AsyncStatus
field in the Communication Protocol register to 1.
Keeps track of the amount of time that has elapsed
since the last SyncIn trigger event. If the SyncIn pin is
connected to the PPS (Pulse Per Second) line on a GPS
and the AsyncStatus field in the Communication
Protocol Register is set to 1, then each asynchronous
measurement will be time stamped relative to the last
received GPS measurement.
Keeps track of the number of times that the SyncOut
trigger event has occurred. This register can be used to
index subsequent measurement outputs, which is
particularly useful when logging sensor data.

Writing zero to the SyncInCount or the SyncOutCount will reset the status counter. Any other value
other than zero will not have an effect. The SyncInTime is read only and cannot be reset to zero.

UM001

5.4

Factory Defaults

Settings Name
User Tag
Serial Baud Rate
Async Data Output Frequency
Async Data Output Type
Synchronization Control
Communication Protocol Control
Binary Output Register 1
Binary Output Register 2
Binary Output Register 3

Default Factory Value
NULL (Empty string)
115200
40 Hz
INS_LLA
3,0,0,0,6,1,0,100000000,0
0,0,0,0,1,0,1
0, 0, 0
0, 0, 0
0, 0, 0

UM001

5.5

Command Prompt

The command prompt provides a fast and simple means of configuring and monitoring the status of the
sensor by typing commands to the unit using the serial port.

5.5.1

List Available Commands

Commands for the System subsystem can be accessed by typing in ‘system’ at the command prompt. To
view all available commands, type ‘system ?’. Below is a view of a terminal window showing a list of the
available commands.
system ?
System Module Commands:
Command:
-------info
comm
errors
reset
save
restore

5.5.2

Description:
----------------------------------------Device specific information such as serial number and firmware version.
Information on the communication interfaces.
Overview of the logged system errors.
Perform a software reset on the unit.
Save register settings to flash memory.
Restore register settings to their factory default state.

System Info

system info
--------------------------------

System Info

Hardware:
Product Model:
Serial Number:
MCU Serial Number:
Hardware Revision:
Form Revision:

VN-310
100013003
34323439044731322F002100
2
1

Software:
Firmware Version:
Revision:
Build Number:

0.3.0.0
691
2813

---------------------------------

--------------------------------------------------------------------------------

5.5.3

System Comm

system comm
----------------------

System Communication Interfaces

Communication Stats:
Serial Messages Parsed
Spi Messages Parsed
Max Serial RX Buffer Usage
Max Serial TX Buffer Usage
Max Spi RX Buffer Usage
Max Spi TX Buffer Usage

UM001

:
:
:
:
:
:

-----------------------

29
0
0
4
0
0

Current Serial 1 TX Bandwidth Usage : 00.0
Current Serial 2 TX Bandwidth Usage : 49.3
Max Serial 1 TX Bandwidth Usage : 49.3
Max Serial 2 TX Bandwidth Usage : 50.5
Min Serial 1 TX Bandwidth Usage : 00.0
Min Serial 2 TX Bandwidth Usage : 48.1
--------------------------------------------------------------------------------

5.5.4

System Errors

system errors
-------------------------------

System Errors

Hard Fault Exceptions
Serial Input Buffer Overflow
Serial Output Buffer Overflow
Serial Insufficient Bandwidth
Invalid Checksums
Invalid Commands
Input Error - Too Few Parameters
Input Error - Too Many Parameters
Input Error - Invalid Parameter
Input Error - Invalid Register
Input Error - Unauthorized Access
Input Error - Watchdog Reset

:
:
:
:
:
:
:
:
:
:
:
:

--------------------------------

0
0
0
0
6
2
0
0
0
0
2
0

--------------------------------------------------------------------------------

5.5.5

System Reset

system reset

5.5.6

System Save

system save

UM001

IMU Subsystem

6.1

IMU Measurement Registers

6.1.1

IMU Measurements

This register provides direct access to the calibrated magnetometer, accelerometer, gyro, barometric
pressure, and temperature measurements available from the onboard IMU.
Register ID :
Comment :
Size (Bytes):
Example Read
Response:
Offset
Name
0
MagX
4
MagY
8
MagZ
12
AccelX
16
AccelY
20
AccelZ
24
GyroX
28
GyroY
32
GyroZ
36
Temp
40
Pressure

IMU Measurements
54
Async Header : IMU
Access : Read Only
Provides the calibrated IMU measurements including barometric pressure.
44
$VNRRG,54,-02.0841,+00.6045,+02.8911,+00.381,-00.154,-09.657,-00.005683,
+00.000262,+00.001475,+21.6,+00099.761*5B
Format
Unit
Description
float
Gauss Uncompensated Magnetic X-axis.
float
Gauss Uncompensated Magnetic Y-axis.
float
Gauss Uncompensated Magnetic Z-axis.
float
m/s2
Uncompensated Acceleration X-axis.
float
m/s2
Uncompensated Acceleration Y-axis.
float
m/s2
Uncompensated Acceleration Z-axis.
float
rad/s Uncompensated Angular rate X-axis.
float
rad/s Uncompensated Angular rate Y-axis.
float
rad/s Uncompensated Angular rate Z-axis.
float
C
IMU Temperature.
float
kPa
Barometric pressure.

You can configure the device to output this register at a fixed rate using the Async Data Output Type
Register in the System subsystem. Once configured the data in this register will be sent out with the
$VNIMU header.

UM001

6.1.2

Delta Theta and Delta Velocity

Delta Theta and Delta Velocity
Register ID : 80
Async Header: DTV
Access : Read
Comment : This register contains the output values of the onboard coning and sculling algorithm.
Size (Bytes): 28
Example Response: $VNRRG,80,+0.665016,-000.119,-000.409,-000.025,+000.011,-000.084,-006.702*6A
Offset
Name
Format
Unit
Description
0
DeltaTime
float
sec
Delta time for the integration interval
4
DeltaThetaX
float
deg
Delta rotation vector component in the x-axis.
8
DeltaThetaY
float
deg
Delta rotation vector component in the y-axis.
12
DeltaThetaZ
float
deg
Delta rotation vector component in the z-axis.
16
DeltaVelocityX
float
m/s
Delta velocity vector component in the x-axis.
20
DeltaVelocityY
float
m/s
Delta velocity vector component in the y-axis.
24
DeltaVelocityZ
float
m/s
Delta velocity vector component in the z-axis.

The Delta Theta and Delta Velocity register contains the computed outputs from the onboard coning and
sculling algorithm. The coning and sculling integrations are performed at the IMU sample rate (nominally
at 800Hz) and reset when the register data is output. If polling this register, the values will represent the
delta time, angles, and velocity since the register was last polled. If the Delta Theta/Velocity data is
selected for asynchronous output via the Async Data Output Type register (Register 6, type 30), the
integrals will be reset each time the data is asynchronously output at the configured rate.
The delta time output contains the length of the time interval over which the deltas were calculated. This
can be used to check the interval time or to compute nonlinear “average” rates and accelerations from
the integrated values.
The delta theta is output as a principal rotation vector, defined as the product of the unit vector of the
principal rotation axis and the principal rotation angle in degrees. For small rotations, a typical use case
for delta angles, the principal rotation vector elements may be treated individually as rotations in degrees
about the individual sensor axes (in any Euler rotation sequence) with little error.
The delta velocity output provides the integration of the acceleration in the chosen frame, taking into
account the coupling effects of any simultaneous rotation experienced.
The coning and sculling algorithm can be configured to operate in multiple frames and with a variety of
compensations applied. See the Delta Theta and Delta Velocity Configuration Register in the IMU
subsystem for further details.
You can configure the device to output this register at a fixed rate using the Async Data Output Type
Register in the System subsystem. Once configured the data in this register will be sent out with the
$VNDTV header.

UM001

6.2
6.2.1

IMU Configuration Registers
Magnetometer Compensation

Register ID :
Comment :
Size (Bytes):
Example Command:
Offset Name
0
C[0,0]
4
C[0,1]
8
C[0,2]
12
C[1,0]
16
C[1,1]
20
C[1,2]
24
C[2,0]
28
C[2,1]
32
C[2,2]
36
B[0]
40
B[1]
44
B[2]

Magnetometer Compensation
23
Access: Read / Write
Allows the magnetometer to be compensated for hard/soft iron effects.
48
$VNRRG,23,1,0,0,0,1,0,0,0,1,0,0,0*73
Format
Unit
Description
float
float
float
float
float
float
float
float
float
float
Gauss
float
Gauss
float
Gauss

This register contains twelve values representing the hard and soft iron compensation parameters. The
magnetic measurements are compensated for both hard and soft iron using the following model. Under
normal circumstances this register can be left in its factory default state. In the event that there are
disturbances in the magnetic field due to hard or soft iron effects, then these registers allow for further
compensation. These registers can also be used to compensate for significant changes to the
magnetometer bias, gain, and axis alignment during installation. Note that this magnetometer
compensation is separate from the compensation that occurs during the calibration process at the factory.
Setting this register to the default state of an identity matrix and zero offset will not eliminate the
magnetometer gain, bias, and axis alignment that occur during factory calibration. These registers only
need to be changed from their default values in the event that hard/soft iron compensation needs to be
performed, or changes in bias, gain, and axis alignment have occurred at some point between the times
the chip was calibrated at the factory and when it is used in the field.
𝑋
𝐶00 𝐶01 𝐶02 𝑀𝑋 − 𝐵0
{𝑌 } = [𝐶10 𝐶11 𝐶12] ∙ {𝑀𝑌 − 𝐵1}
𝑍
𝐶20 𝐶21 𝐶22
𝑀𝑍 − 𝐵2
The variables {𝑀𝑋, 𝑀𝑌, 𝑀𝑍} are components of the measured magnetic field. The {X, Y, Z} variables are
the new magnetic field measurements outputted after compensation for hard/soft iron effects. All twelve
numbers are represented by single-precision floating points.

UM001

6.2.2

Acceleration Compensation

Register ID :
Comment :
Size (Bytes):
Example Command:
Offset Name
0
C[0,0]
4
C[0,1]
8
C[0,2]
12
C[1,0]
16
C[1,1]
20
C[1,2]
24
C[2,0]
28
C[2,1]
32
C[2,2]
36
B[0]
40
B[1]
44
B[2]

Accelerometer Compensation
25
Access : Read / Write
Allows the accelerometer to be further compensated for scale factor, misalignment, and
bias errors.
48
$VNRRG,25,1,0,0,0,1,0,0,0,1,0,0,0*75
Format
Unit Description
float
float
float
float
float
float
float
float
float
float
m/s2
float
m/s2
float
m/s2

This register contains twelve values representing the accelerometer compensation parameters. The
accelerometer measurements are compensated for changes in bias, gain, and axis alignment that can
occur during the installation of the chip on the customer’s board using the following model. Under normal
circumstances this register can be left in its factory default state. In the event that there are significant
changes to the accelerometer bias, gain, and axis alignment during installation, then these registers allow
for further compensation. Note that this accelerometer compensation is separate from the compensation
that occurs during the calibration process at the factory. Setting this register to the default state of an
identity matrix and zero offset will not eliminate the accelerometer gain, bias, and axis alignment that
occur during factory calibration. These registers only need to be changed from their default values in the
event that changes in bias, gain, and axis alignment have occurred at some point between the times the
chip was calibrated at the factory and when it is used in the field.
𝑋
𝐶00 𝐶01 𝐶02 𝐴𝑋 − 𝐵0
{𝑌 } = [𝐶10 𝐶11 𝐶12] ∙ {𝐴𝑌 − 𝐵1}
𝑍
𝐶20 𝐶21 𝐶22
𝐴𝑍 − 𝐵2
The variables {AX,AY,AZ} are components of the measured acceleration. The {X, Y, Z} variables are the
new acceleration measurements outputted after compensation for changes during sensor mounting. All
twelve numbers are represented by single-precision floating points.

UM001

6.2.3

Gyro Compensation

Register ID :
Comment :
Size (Bytes):
Example Command:
Offset Name
0
C[0,0]
4
C[0,1]
8
C[0,2]
12
C[1,0]
16
C[1,1]
20
C[1,2]
24
C[2,0]
28
C[2,1]
32
C[2,2]
36
B[0]
40
B[1]
44
B[2]

Gyro Compensation
84
Access : Read / Write
Allows the gyro to be further compensated for scale factor, misalignment, and bias errors.
48
$VNRRG,84,1,0,0,0,1,0,0,0,1,0,0,0*7E
Format
Unit Description
float
float
float
float
float
float
float
float
float
float
rad/s
float
rad/s
float
rad/s

This register contains twelve values representing the gyro compensation parameters. The gyro
measurements are compensated for changes in bias, gain, and axis alignment that can occur during the
installation of the chip on the customer’s board using the following model. Under normal circumstances
this register can be left in its factory default state. In the event that there are significant changes to the
gyro bias, gain, and axis alignment during installation or during the life of the part; these registers allow
for further compensation. Note that this gyro compensation is separate from the compensation that
occurs during the calibration process at the factory. Setting this register to the default state of an identity
matrix and zero offset will not eliminate the gyro gain, bias, and axis alignment that occur during factory
calibration. These registers only need to be changed from their default values in the event that changes
in bias, gain, and axis alignment have occurred at some point between the times the chip was calibrated
at the factory and when it is used in the field.
𝑋
𝐶00 𝐶01 𝐶02 𝐺𝑋 − 𝐵0
{𝑌 } = [𝐶10 𝐶11 𝐶12] ∙ {𝐺𝑌 − 𝐵1}
𝑍
𝐶20 𝐶21 𝐶22
𝐺𝑍 − 𝐵2
The variables {GX, GY, GZ}IMU are components of the measured angular rate. The {GX, GY, GZ}Comp variables
are the new acceleration measurements outputted after compensation for changes during sensor
mounting. All twelve numbers are represented by single-precision floating points.

UM001

6.2.4

Reference Frame Rotation

Register ID :
Comment :
Size (Bytes):
Example Response:
Offset Name
0
C[0,0]
4
C[0,1]
8
C[0,2]
12
C[1,0]
16
C[1,1]
20
C[1,2]
24
C[2,0]
28
C[2,1]
32
C[2,2]

Reference Frame Rotation
26
Access : Read / Write
Allows the measurements of the VN-100 to be rotated into a different reference frame.
36
$VNRRG,26,1,0,0,0,1,0,0,0,1*6A
Format Unit Description
float
float
float
float
float
float
float
float
float
-

This register contains a transformation matrix that allows for the transformation of measured
acceleration, magnetic, and angular rates from the body frame of the VN-100 to any other arbitrary frame
of reference. The use of this register allows for the sensor to be placed in any arbitrary orientation with
respect to the user’s desired body coordinate frame. This register can also be used to correct for any
orientation errors due to mounting the VN-100 on the user’s vehicle or platform.
𝑋
𝐶00 𝐶01 𝐶02 𝑋
{𝑌 } = [𝐶10 𝐶11 𝐶12] ∙ {𝑌 }
𝑍 𝑈
𝐶20 𝐶21 𝐶22
𝑍 𝐵
The variables {𝑋, 𝑌, 𝑍}𝐵 are a measured parameter such as acceleration in the body reference frame with
respect to the VN-100. The variables {𝑋, 𝑌, 𝑍}𝑈 are a measured parameter such as acceleration in the
user’s frame of reference. The reference frame rotation register thus needs to be loaded with the
transformation matrix that will transform measurements from the body reference frame of the VN-100
to the desired user frame of reference.

The matrix C in the Reference Frame Rotation Register must be an orthonormal, right-handed matrix.
The sensor will output an error if the tolerance is not within 1e-5. The sensor will also report an error
if any of the parameters are greater than 1 or less than -1.

UM001

6.2.5

IMU Filtering Configuration

IMU Filtering Configuration
Register ID : 85
Access : Read / Write
Comment : Controls the level of filtering performed on the raw IMU measurements.
Size (Bytes): 15
Example Response: $VNRRG,85,0,5,5,5,0,0,3,3,3,0*78
Offset
Name
Format
Unit
Description
0
MagWindowSize
uint16
Number of previous measurements averaged for magnetic
measurements.
2
AccelWindowSize
uint16
Number of previous measurements averaged for
acceleration measurements.
4
GyroWindowSize
uint16
Number of previous measurements averaged for gyro
measurements.
6
TempWindowSize
uint16
Number of previous measurements averaged for
temperature measurements.
8
PresWindowSize
uint16
Number of previous measurements averaged for pressure
measurements.
10
MagFilterMode
uint8
Filtering mode for magnetic measurements.
See table below for options.
11
AccelFilterMode
uint8
Filtering mode for acceleration measurements.
See table below for options.
12
GyroFilterMode
uint8
Filtering mode for gyro measurements.
See table below for options.
13
TempFilterMode
uint8
Filtering mode for temperature measurements.
See table below for options.
14
PresFilterMode
uint8
Filtering mode for pressure measurements.
See table below for options.

This register allows the user to configure the FIR filtering what is applied to the IMU measurements. The
filter is a uniformly-weighted moving window (boxcar) filter of configurable size. The filtering does not
affect the values used by the internal filter, but only the output values.

WindowSize
The WindowSize parameters for each sensor define the number of samples at the IMU rate (default
400Hz) which will be averaged for each output measurement.

FilterMode
The FilterMode parameters for each sensor select which output quantities the filtering should be applied
to. Filtering can be applied to either the uncompensated IMU measurements, compensated (HSI and
biases compensated by onboard filters, if applicable), or both.
IMU Filtering Modes
Value
0
1
2
3

UM001

Description
No Filtering
Filtering performed only on raw uncompensated IMU measurements.
Filtering performed only on compensated IMU measurements.
Filtering performed on both uncompensated and compensated IMU measurements.

6.2.6

Delta Theta and Delta Velocity Configuration

Delta Theta and Delta Velocity Configuration
Register ID : 82
Access : Read / Write
Comment : This register contains configuration options for the internal coning/sculling calculations
Size (Bytes): 6
Example Response: $VNRRG,82,0,0,0,0,0*65
Offset
Name
Format
Unit
Description
0
IntegrationFrame
uint8
Output frame for delta velocity quantities
1
GyroCompensation
uint8
Compensation to apply to angular rate
2
AccelCompensation
uint8
Compensation(s) to apply to accelerations
3
Reserved
uint8
Reserved for future use. Should be set to 0.
4
Reserved
uint16
Reserved for future use. Should be set to 0.

The Delta Theta and Delta Velocity Configuration register allows configuration of the onboard coning and
sculling used to generate integrated motion values from the angular rate and acceleration IMU quantities.
The fully-coupled coning and sculling integrals are computed at the IMU sample rate (nominal 400 Hz).

IntegrationFrame
The IntegrationFrame register setting selects the reference frame used for coning and sculling. Note that
using any frame other than the body frame will rely on the onboard Kalman filter’s attitude estimate. The
factory default state is to integrate in the sensor body frame.
IntegrationFrame
Value
0
1
2

Description
Body frame
NED frame
ECEF frame

GyroCompensation
The GyroCompensation register setting selects the compensation to be applied to the angular rate
measurements before integration. If bias compensation is selected, the onboard Kalman filter’s real-time
estimate of the gyro biases will be used to compensate the IMU measurements before integration. The
factory default state is to integrate the uncompensated angular rates from the IMU.
GyroCompensation
Value
0
1

Description
None
Bias

UM001

AccelCompensation
The AccelCompensation register setting selects the compensation to be applied to the acceleration
measurements before integration. If bias compensation is selected, the onboard Kalman filter’s real-time
estimate of the accel biases will be used to compensate the IMU measurements before integration. The
factory default state is to integrate the uncompensated acceleration from the IMU.
AccelCompensation
Value
0
1

UM001

Description
None
Bias

6.3

Factory Defaults

Settings Name
Magnetometer Compensation
Accelerometer Compensation
Gyro Compensation
Reference Frame Rotation
IMU Filtering Configuration
Delta Theta and Delta Velocity
Configuration

Default Factory Value
1,0,0,0,1,0,0,0,1,0,0,0
1,0,0,0,1,0,0,0,1,0,0,0
1,0,0,0,1,0,0,0,1,0,0,0
1,0,0,0,1,0,0,0,1
0,4,4,4,0,0,3,3,3,0
0,0,0,0,0

UM001

6.4

Command Prompt

The command prompt provides a fast and simple means of configuring and monitoring the status of the
sensor by typing commands to the unit using the serial port.

6.4.1

List Available Commands

Commands for the System subsystem can be accessed by typing in ‘imu’ at the command prompt. To
view all available commands, type ‘imu ?’. Below is a view of a terminal window showing a list of the
available commands.
imu ?
Imu Module Commands:
Command:
-------info
meas

6.4.2

Description:
-------------------------------------------------------------------Imu specific information such as serial number and firmware version.
Current Imu measurement, and run-time statistics.

IMU Info

imu info
------------------------------

Imu Information

-------------------------------

Magnetometer - HSI Settings (Register 44)
Mode : Using Onboard
Magnetometer - User
+01.000 +00.000
+00.000 +01.000
+00.000 +00.000

HSI Calibration (Register 23)
+00.000 +00.000
+00.000 +00.000
+01.000 +00.000

Magnetometer - Onboard HSI Calibration (Register 47)
+01.000 +00.000 +00.000 -00.000
+00.000 +01.000 +00.000 -00.000
+00.000 +00.000 +01.000 -00.000
Accelerometer - User Calibration (Register 25)
+01.000 +00.000 +00.000 +00.000
+00.000 +01.000 +00.000 +00.000
+00.000 +00.000 +01.000 +00.000
Sensor Self Test: (performed at startup)
Mag
: Passed
Accel : Passed
Gyro : Passed
Pres : Passed
--------------------------------------------------------------------------------

UM001

6.4.3

IMU Meas

imu meas
-----------------------------Current Sensor Measurements:
Mag X
: -000.866 [Gauss]
Mag Y
: +001.016 [Gauss]
Mag Z
: +002.365 [Gauss]
Acel X
: +004.178 [m/s]
Acel Y
: -000.637 [m/s]
Acel Z
: -008.927 [m/s]
Gyro X
: -000.417 [deg/s]
Gyro Y
: +000.668 [deg/s]
Gyro Z
: -001.102 [deg/s]
Temp
: +027.94 [C]
Temp Rate: +0.04 [C/min]
Pres
: +101.36 [kPa]

Imu Measurement

Current Sensor Noise:
Sensor
Units
Mag
mGauss
Accel
mg
Gyro
deg/s
Temp
C
Pres
Pa

(measured
X-Axis
+03.228
+01.854
+0.0631
+0.0026
+007.36

over last
Y-Axis
+02.934
+02.115
+0.0544

Minimum Sensor Noise:
Sensor
Units
Mag
mGauss
Accel
mg
Gyro
deg/s
Temp
C
Pres
Pa

(since startup)
X-Axis
Y-Axis
+02.877
+02.659
+01.785
+01.966
+0.0587
+0.0487
+0.0011
+006.13

-------------------------------

5 seconds)
Z-Axis
+04.159
+02.872
+0.0580

Z-Axis
+03.673
+02.599
+0.0537

Minimum Sensor Measurement: (since startup)
Sensor
Units
X-Axis
Y-Axis
Z-Axis
Mag
Gauss
-00.236
+00.244
+00.577
Accel
g
+00.414
-00.077
-00.949
Gyro
deg/s
-002.92
-005.33
-002.03
Temp
C
+27.83
Pres
kPa
+101.30
Maximum Sensor Measurement: (since startup)
Sensor
Units
X-Axis
Y-Axis
Z-Axis
Mag
Gauss
+00.000
+00.271
+00.611
Accel
g
+00.439
+00.000
+00.000
Gyro
deg/s
+002.02
+006.44
+000.00
Temp
C
+28.01
Pres
kPa
+101.38
Sensor Saturation Events: (since startup)
Sensor
X-Axis
Y-Axis
Z-Axis
Mag
0
0
0
Accel
0
0
0
Gyro
0
0
0
Pressure 0
Temp
0
--------------------------------------------------------------------------------

UM001

Attitude Subsystem

7.1
7.1.1

Commands
Known Magnetic Disturbance Command

This command is used to notify the VN-100 that a magnetic disturbance is present. When the VN-100
receives this command it will tune out the magnetometer and will pause the current hard/soft iron
calibration if it is enabled. A single parameter is provided to tell the VN-100 whether the disturbance is
present or not.
0 – No Disturbance is present
1 – Disturbance is present
Example Magnetic Disturbance Command

7.1.2

Example Command

Message

UART Command
UART Response
SPI Command (8 bytes)
SPI Response (8 bytes)

$VNKMD,1*47
$VNKMD,1*47
08 01 00 00 (shown as hex)
00 08 01 00 (shown as hex)

Known Acceleration Disturbance Command

This command is used to notify the VN-100 that an acceleration disturbance is present. When the VN100 receives this command it will tune out the accelerometer. A single parameter is provided to tell the
VN-100 whether the disturbance is present or not.
0 – No Disturbance is present
1 – Disturbance is present
Example Acceleration Disturbance Command

7.1.3

Example Command

Message

UART Command
UART Response
SPI Command (8 bytes)
SPI Response (8 bytes)

$VNKAD,1*4B
$VNKAD,1*4B
09 01 00 00 (shown as hex)
00 09 01 00 (shown as hex)

Set Gyro Bias Command

This command will instruct the VN-100 to copy the current gyro bias estimates into register 74. After
sending this command you will need to issue the write settings command in the System subsystem to save
the state of this register to flash memory. Once saved the VN-100 will use these bias estimates as the
initial state at startup.
Example Gyro Bias Command
Example Command

UM001

Message

UART Command
UART Response
SPI Command (8 bytes)
SPI Response (8 bytes)

7.2

Measurement Registers

7.2.1

Yaw Pitch Roll
Register ID :
Comment :

Offset
0
4
8

$VNSGB*XX
$VNSGB*XX
0C 00 00 00 (shown as hex)
00 0C 00 00 (shown as hex)

Size (Bytes):
Example Response:
Name
Yaw
Pitch
Roll

Yaw, Pitch, and Roll
8
Async Header : YPR
Access : Read Only
Attitude solution as yaw, pitch, and roll in degrees. The yaw, pitch, and roll is
given as a 3,2,1 Euler angle rotation sequence describing the orientation of the
sensor with respect to the inertial North East Down (NED) frame.
12
$VNRRG,8,+006.271,+000.031,-002.000*66
Format Unit Description
float
deg
Yaw angle.
float
deg
Pitch angle.
float
deg
Roll angle.

UM001

7.2.2

Offset
0
4
8
12

Attitude Quaternion

Quaternion
9
Async Header : QTN
Access : Read Only
Attitude solution as a quaternion.
16
$VNRRG,9,-0.017386,-0.000303,+0.055490,+0.998308*4F
Format Unit Description
float
Calculated attitude as quaternion.
float
Calculated attitude as quaternion.
float
Calculated attitude as quaternion.
float
Calculated attitude as quaternion. Scalar component.

UM001

7.2.3

Offset
0
4
8
12
16
20
24
28
32
36
40
44

Yaw, Pitch, Roll, Magnetic, Acceleration, and Angular Rates

Yaw, Pitch, Roll, Magnetic, Acceleration, and Angular Rates
Register ID : 27
Async Header : YMR
Access : Read Only
Comment : Attitude solution, magnetic, acceleration, and compensated angular rates.
Size (Bytes): 48
Example Response: $VNRRG,27,+006.380,+000.023,-001.953,+1.0640,0.2531,+3.0614,+00.005,+00.344,-09.758,-0.001222,-0.000450,-0.001218*4F
Name
Format Unit
Description
Yaw
float
deg
Calculated attitude heading angle in degrees.
Pitch
float
deg
Calculated attitude pitch angle in degrees.
Roll
float
deg
Calculated attitude roll angle in degrees.
MagX
float
Gauss Compensated magnetometer measurement in x-axis.
MagY
float
Gauss Compensated magnetometer measurement in y-axis.
MagZ
float
Gauss Compensated magnetometer measurement in z-axis.
AccelX
float
m/s2
Compensated accelerometer measurement in x-axis.
AccelY
float
m/s2
Compensated accelerometer measurement in y-axis.
AccelZ
float
m/s2
Compensated accelerometer measurement in z-axis.
GyroX
float
rad/s Compensated angular rate in x-axis.
GyroY
float
rad/s Compensated angular rate in y-axis.
GyroZ
float
rad/s Compensated angular rate in z-axis.

UM001

7.2.4

Quaternion, Magnetic, Acceleration and Angular Rates

Name
Quat[0]
Quat[1]
Quat[2]
Quat[3]
MagX
MagY
MagZ
AccelX
AccelY
AccelZ
GyroX
GyroY
GyroZ

Quaternion, Magnetic, Acceleration, and Angular Rates
15
Async Header : QMR
Access : Read Only
Attitude solution, magnetic, acceleration, and compensated angular rates.
52
$VNRRG,15,-0.017057,-0.000767,+0.056534,+0.998255,+1.0670,-0.2568,+3.0696,00.019,+00.320,-09.802,-0.002801,-0.001186,-0.001582*65
Format Unit
Description
float
Calculated attitude as quaternion.
float
Calculated attitude as quaternion.
float
Calculated attitude as quaternion.
float
Calculated attitude as quaternion. Scalar component.
float
Gauss Compensated magnetometer measurement in x-axis.
float
Gauss Compensated magnetometer measurement in y-axis.
float
Gauss Compensated magnetometer measurement in z-axis.
float
m/s2
Compensated accelerometer measurement in x-axis.
float
m/s2
Compensated accelerometer measurement in y-axis.
2
float
m/s
Compensated accelerometer measurement in z-axis.
float
rad/s Compensated angular rate in x-axis.
float
rad/s Compensated angular rate in y-axis.
float
rad/s Compensated angular rate in z-axis.

UM001

7.2.5

Magnetic Measurements

Magnetic Measurements
17
Async Header : MAG
Access : Read Only
Magnetometer measurements.
12
$VNRRG,17,+1.0647,-0.2498,+3.0628*66
Format
Unit
Description
float
Gauss Compensated magnetometer measurement in x-axis.
float
Gauss Compensated magnetometer measurement in y-axis.
float
Gauss Compensated magnetometer measurement in z-axis.

UM001

7.2.6

Acceleration Measurements

Acceleration Measurements
18
Async Header : ACC
Access : Read Only
Acceleration measurements.
12
$VNRRG,18,+00.013,+00.354,-09.801*65
Format
Unit Description
float
m/s2 Compensated accelerometer measurement in x-axis.
float
m/s2 Compensated accelerometer measurement in y-axis.
float
m/s2 Compensated accelerometer measurement in z-axis.

UM001

7.2.7

Angular Rate Measurements

Angular Rate Measurements
19
Async Header : GYR
Access :
Compensated angular rates.
12
$VNRRG,19,+0.002112,-0.000362,-0.000876*6C
Format
Unit
Description
float
rad/s Compensated angular rate in x-axis.
float
rad/s Compensated angular rate in y-axis.
float
rad/s Compensated angular rate in z-axis.

Read Only

UM001

7.2.8

Magnetic, Acceleration and Angular Rates

Name
MagX
MagY
MagZ
AccelX
AccelY
AccelZ
GyroX
GyroY
GyroZ

Magnetic, Acceleration, and Angular Rates
20
Async Header : MAR
Access : Read Only
Magnetic, acceleration, and compensated angular rates.
36
$VNRRG,20,+1.0684,-0.2578,+3.0649,-00.005,+00.341,-09.780,-0.000963,+0.000840,0.000466*64
Format Unit
Description
float
Gauss Compensated magnetometer measurement in x-axis.
float
Gauss Compensated magnetometer measurement in y-axis.
float
Gauss Compensated magnetometer measurement in z-axis.
float
m/s2
Compensated accelerometer measurement in x-axis.
float
m/s2
Compensated accelerometer measurement in y-axis.
float
m/s2
Compensated accelerometer measurement in z-axis.
float
rad/s Compensated angular rate in x-axis.
float
rad/s Compensated angular rate in y-axis.
float
rad/s Compensated angular rate in z-axis.

UM001

7.3

Configuration Registers

7.3.1

VPE Basic Control

VPE Basic Control
35
Firmware : v1.0.0.0
Access : Read / Write
Provides control over various features relating to the onboard attitude filtering
algorithm.
4
$VNRRG,35,1,3,1,1*77
Format Unit Description
uint8
Enable / Disable the Vector Processing Engine (VPE).
uint8
Heading mode used by the VPE.
uint8
Filtering Mode used by the VPE.
uint8
Tuning Mode used by the VPE.
Enable
Value
0
1

State
DISABLE
ENABLE

HeadingMode
Value
0
1
2

Mode
Absolute Heading
Relative Heading
Indoor Heading
Filtering Mode

Value
0
1

Mode
OFF
MODE 1
Tuning Mode

Value
0
1

100

Mode
OFF
MODE 1

UM001

Hard/Soft Iron Estimator Subsystem

8.1

Configuration Registers

8.1.1

Magnetometer Calibration Control

Magnetometer Calibration Control
44
Access : Read / Write
Controls the magnetometer real-time calibration algorithm.
4
$VNRRG,44,1,2,5*69
Format Unit
Description
uint8
Controls the mode of operation for the onboard real-time
magnetometer hard/soft iron compensation algorithm.
HSIOutput
uint8
Controls the type of measurements that are provided as
outputs from the magnetometer sensor and also subsequently
used in the attitude filter.
ConvergeRate
uint8
Controls how quickly the hard/soft iron solution is allowed to
converge onto a new solution. The slower the convergence
the more accurate the estimate of the hard/soft iron solution.
A quicker convergence will provide a less accurate estimate of
the hard/soft iron parameters, but for applications where the
hard/soft iron changes rapidly may provide a more accurate
attitude estimate.
Range: 1 to 5
1 = Solution converges slowly over approximately 60-90
seconds.
5 = Solution converges rapidly over approximately 15-20
seconds.

Table 2 – HSI_Mode Field
Mode
HSI_OFF
HSI_RUN

Value
0
1

HSI_RESET

Description
Real-time hard/soft iron calibration algorithm is turned off.
Runs the real-time hard/soft iron calibration. The algorithm will continue using its existing
solution. The algorithm can be started and stopped at any time by switching between the
HSI_OFF and HSI_RUN state.
Resets the real-time hard/soft iron solution.
Table 3 – HSI_Output Field

Mode
NO_ONBOARD
USE_ONBOARD

UM001

Value
1
3

Description
Onboard HSI is not applied to the magnetic measurements.
Onboard HSI is applied to the magnetic measurements.

101

8.2
8.2.1

Status Registers
Calculated Magnetometer Calibration

Register ID :
Comment :
Size (Bytes):
Example Response:
Offset
Name
0
C[0,0]
4
C[0,1]
8
C[0,2]
12
C[1,0]
16
C[1,1]
20
C[1,2]
24
C[2,0]
28
C[2,1]
32
C[2,2]
36
B[0]
40
B[1]
44
B[2]

Calculated Magnetometer Calibration
47
Calculated magnetometer calibration values.
48
$VNRRG,46,1,0,0,0,1,0,0,0,1,0,0,0*70
Format
Unit
Description
float
float
float
float
float
float
float
float
float
float
float
float
-

Access :

Read Only

This register contains twelve values representing the calculated hard and soft iron compensation
parameters. The magnetic measurements are compensated for both hard and soft iron using the
following model.
𝑋
𝐶00 𝐶01 𝐶02 𝑀𝑋 − 𝐵0
{𝑌 } = [𝐶10 𝐶11 𝐶12] ∙ {𝑀𝑌 − 𝐵1}
𝑍
𝐶20 𝐶21 𝐶22
𝑀𝑍 − 𝐵2
The variables {𝑀𝑋, 𝑀𝑌, 𝑀𝑍} are components of the measured magnetic field. The {X, Y, Z} variables are
the new magnetic field measurements outputted after compensation for hard/soft iron effects.

102

UM001

8.3

Factory Defaults

Settings Name
Magnetometer Calibration Control

UM001

Default Factory Value
1,3,5

103

8.4

Command Prompt

The command prompt provides a fast and simple means of configuring and monitoring the status of the
sensor by typing commands to the unit using the serial port.

8.4.1

List Available Commands

Commands for the System subsystem can be accessed by typing in ‘hsi’ at the command prompt. To view
all available commands, type ‘hsi ?’. Below is a view of a terminal window showing a list of the available
commands.
hsi ?
Hard/Soft Iron Estimator Module Commands:
Command:
-------info
plotInput
plotOutput

Description:
-------------------------------------------------------------------Estimator state information and configuration settings.
Plot onboard HSI Input.
Plot onboard HSI Output.

8.4.2 Info
hsi info
----------------- Hard/Soft Iron Estimator State Information
Magnetometer Calibration Control (Register 44):

-----------------

HsiMode: Run
OutMode: Use Onboard
ConvergeRate: 5
Magnetometer Calibration Status (Register 46):
LastBin: 0
NumMeas: 102
AvgResidual: 0.014
LastMeas: +0.599 +0.538
Bins[0]: 215
Bins[1]: 188
Bins[2]: 135
Bins[3]: 47
Bins[4]: 198
Bins[5]: 231
Bins[6]: 202

+2.910

Calculated Magnetometer Calibration (Register 47):
+00.966
+00.000
+00.000

+00.000
+00.966
+00.000

+00.000
+00.000
+00.966

-00.215
-00.179
-00.077

Num Measurements: 358
Filter Run Count: 358
Mag Uncertainty : 0.00
--------------------------------------------------------------------------------

104

UM001

8.4.3 PlotInput
hsi plotinput
---------------------

HSI Estimator Magnetic Input Plot

----------------------

Uncalibrated XY
+-------------------+-------------------+-------------------+-------------------+
|
|
* * * | *
*
|
|
|
|
**** * * * *
***
|
|
|
| * *
*
*
|
** |
|
|
* * * *
*
|* *
*
|
|
|
*** ** *
*
* **
*
|
|
|
*** |
*
* * *
* |
**
*
|
|
*
|* *
** * *
|
*
* *
|*
*
|
|
*
|
*
*|
*
|
|
|
*
*|
* *
* |
*
**
*
|
+---------***-------+-----------*-------*----*--*-----*-----+----------*--------+
|
*
| *
*
*
*
|
**
|
|
* *
*
| *
*
***
|
|
* **
*
|
* |
* *
|
|
|
**
|
*
**
|
| *
*
|
|
*
* |
* * *
|
*
|
|
|
***
|
*|
*
* * *
|
*
|
|
*
|
*
*
|
*
|
*
* *
|
|
*
|
*
|
*
| *
*
|
|
*
**
|
| *
*
|
*
|
+---*-*-*-----------+---*---------------+--------*-----*----+*------*-------*---+
|
*
| *
|
*
| *
*
|
| *
*
* |
|
** | *
|
|
|
* *
** *
*|
*
|
*
|
|
*
** *
|
*
*
** *
* *
*
**
**
*
|
|
* *
|
*
* |
|
**
|
|
**
|
*
|
*
|
*
|
|
*
*
*
*
|
* |
*
|
|
**
|
|
*
* |
**
|
|
***
* *
|
|
*
|
***
|
+--------**--------*+-------------------+-------------------+-----***-----------+
|
**** *
|
*
*
* *
*
|*
**
|
|
* * * |
*
|
**
|
|
***
|
|
|
* *
|
|
* |
*
|
* *
|
|
|
*
| *
*
|
|
|
|
|
|
|
|
| *
|
|
|
|
|
|
|
|
|
|
|
|
|
+-------------------+-------------------+-------------------+-------------------+
Plot Center :
Plot Scale :

+0.000,
+1.042,

+0.000
+1.042

--------------------------------------------------------------------------------

UM001

105

8.4.4 PlotOutput
hsi plotoutput
---------------------

HSI Estimator Magnetic Output Plot

---------------------

Calibrated XY
+-------------------+-------------------+-------------------+-------------------+
|
|
|
|
|
|
|
|
|
|
|
|
** * *
*
*
|
|
|
|
*** * * * *
**
|
|
|
|
* *
* *
|
* *|
|
|
|
* * * *
*
| * *
*
|
|
|
| *** ***
*
* ***
*
|
|
|
***
*
** ** |*
|**
*
|
|
*
* *
** * * | *
** * *
| *
*
|
+-----------------*-+--*------*---------+-------------------+-------------------+
|
*
|
* *
*
* *
|*
*
|
|
**
|
* * | **
*
*
|
**
|
|
* *
|
*
| * *
*
|*
**
|
|
* * * | *
*
* * |
*
|
|
**
|
* *
|
|
*
|
|
|
*
* * |
* |
*
|
|
***
| *
*
|
* * ** |
|
|
**
|
|*
*
|
*
*
*
|
|
*
|
* *
*
|
*
|
*
*
|
+----------*----**--+-------------------+---*---*---------*-+---------------**--+
|
*** *
|
*
|
*
* | *
*
*
|
|
**
|
*
|
*
| *
*
|
|
*
*
|*
|
**
*
|
|
*
|
* * *** * | *
*
|
*
|
|
* ****
|
*
|* **
* * *
|**
** *
|
|
*
|
*
*
|
**
|
|
**
|
*
*
|
*
|
*
|
|
*
*
* *
|
*
*
|
|
*
*|
|
*
*
**
|
+-----------***--*--+--*----------------+----------*--------+-------------------+
|
***
|
*
|
*
| *
***
|
|
*
*|*
*| *
*
|
**
|
|
****|
|
|
**
|
|
* |
|
| ** *
|
|
|*
*
|
|
|
|
|
* |
*
*
|
|
|
|
*
|
|
|
|
|
|
|
|
|
|
|
|
|
+-------------------+-------------------+-------------------+-------------------+
Plot Center :
Plot Scale :

+0.000,
+0.946,

+0.000
+0.946

--------------------------------------------------------------------------------

106

UM001

Velocity Aiding

Velocity aiding provides a method to increase performance of an AHRS sensor for applications where the
sensor is subjected to constant accelerations.

9.1

Overview
AHRS Fundamentals

An Attitude Heading Reference System (AHRS) is a sensor system that estimates the attitude of a vehicle
based upon the combined measurements provided by a 3-axis gyroscope, accelerometer, and
magnetometer. An AHRS sensor typically utilizes a Kalman filter to compute the 3D orientation of the
vehicle based upon the vector measurements provided from the accelerometer and the magnetometer.
The accelerometer measures the effect of both gravity and any acceleration due to body motion. The
magnetometer measures the influence of both the earth’s magnetic field and the influence of any nearby
magnetic fields created by nearby ferromagnetic objects. The gyroscope provides an accurate short term
measurement of the relative change in the orientation of the sensor however it is not capable of providing
a measurement of the orientation itself. The absolute accuracy of the heading, pitch and roll solution for
an AHRS is ultimately derived from the accuracy of the vector measurements provided by the
accelerometer and magnetometer.

AHRS Assumptions
Without any form of external compensation an AHRS does not have by itself any means of knowing how
it is moving relative to the fixed Earth. As such it does not have any means of knowing what the actual
acceleration of the body is. Since the accelerometer measures the effect of both gravity and the
acceleration due to motion, the standard AHRS algorithm has to make the assumption that the long-term
acceleration due to motion is zero. With this assumption in place the AHRS know has sufficient
information to estimate the pitch and roll based upon the measurement of gravity provided by the
accelerometer. This assumption works very well for applications where the sensor does not experience
any long-term acceleration such as when it is used indoors or when used on a large marine vessel.
Applications that do experience long-term accelerations due to motion however will experience a
significant error in the pitch and roll solution due to the fact that the assumption of zero body acceleration
in the AHRS algorithm is constantly being violated.
The most common case where this acceleration becomes a significant problem for an AHRS is when it is
used on an aircraft operating in a banked turn. In straight and level flight the AHRS will provide an accurate
measurement of attitude as long as the long-term accelerations are nominally zero. When the aircraft
banks and enters a coordinated turn however, a long-term acceleration is present which due to the
centripetal force created by traveling along a curved path. This apparent force is what makes you feel as
if you are being pushed to the side when you drive around a corner in a car.

Figure 1 - Measured Acceleration in Coordinated Turn

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When an aircraft is in a banked turn the accelerometer will measure gravity plus this centripetal
acceleration which will result in a measurement vector that acts perpendicular to the wings of the aircraft
as shown in the above figure. This will result in the AHRS estimating a roll angle of zero while the aircraft
is in fact in a banked turn and thus has a significant actual roll angle relative to the horizon.
If the AHRS however can obtain some knowledge of this actual motion relative to the fixed Earth then it
is possible for it to subtract out the effect of the centripetal acceleration, resulting in an accurate estimate
of attitude. By providing the AHRS with the known velocity or airspeed it is possible for the AHRS to
estimate the centripetal acceleration term based upon this velocity and the known body angular rates.
Figure 2 - AHRS with Velocity Compensation

The above figure accurately depicts quality of attitude solution provided by three separate types of
attitude estimators while operating in a coordinated turn. The flight display on the far left represents the

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actual attitude which is derived from the flight simulator. Moving from left to right are three separate
types of attitude estimators shown in order based upon the accuracy of their derived solution. The most
accurate solution is proved by the Inertial Navigation System (INS). This type of estimator incorporates
the position and velocity measurements from a GPS along with the accelerometer, and gyroscope in an
optimal fashion to simultaneously estimate attitude and the position and velocity of the vehicle. It
provides the most accurate attitude estimate since it makes no assumptions regarding the accelerometer
measurements.
Measurement Sources for Velocity Aiding
Below are three common sources used for velocity aiding.
Airspeed Sensor
When an airspeed sensor is used for velocity aiding it is important to note which type of airspeed is being
used. Since the airspeed input is being used by the AHRS to estimate the centripical acceleration, the
airspeed used should be ideally close to the actual speed relative to the fixed earth. Normally airspeed
sensors measure the speed of the aircraft relative to the atmosphere, thus there will be a difference
between the speed relative to the fixed Earth and the speed given by the airspeed indicator, equal to the
speed of the atmosphere relative to the ground (wind speed). In high wind conditions this can cause some
increased error in the velocity aiding algorithm.
When using airspeed
Speedometer
For automotive applications the speedometer measurement can be used to perform velocity aiding. The
speedometer measurement will provide the ground speed of the vehicle. There will be some small loss
due to fact that vertical speed is not included, however the effect will be minimal.
GPS
For most applications GPS provides an excellent source of velocity aiding for an AHRS. It is recommended
that you use a GPS receiver with at least a 5Hz update rate.

9.1.1

Tuning for Higher Performance

In most situations the default tuning parameters for the velocity compensation will provide adequate
results without the need for manual adjustment. In the event that you have a case where you need
improved performance, there are tuning parameters provided in the Velocity Compensation Control
Register (Register 50) that provide a means to adjust the behavior of the compensation algorithm.

Velocity Tuning
The velocity tuning field in the Velocity Compensation Control Register in the Velocity Aiding subsystem
provides a means to adjust the uncertainty level used for the velocity measurement in the compensation
estimation filter. The default value is 0.1. A larger value places less trust in the velocity measurements,
while a smaller number will place more trust in the velocity measurement. If your velocity measurement
is noisy or unreliable increasing this number may provide better results. If you have a very accurate
velocity measurement then lowering this number will likely produce better results.

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Velocity Measurement Rate
The performance of the velocity compensation will be affected by both the accuracy of the velocity
measurements and the rate at which they are applied. To ensure adequate performance the velocity
should be provided at a rate higher than 1Hz. Best performance will be achieved with update rates of
10Hz or higher.
If you stop sending velocity measurement updates for any reason, the velocity compensation will
continue indefinitely using the last received velocity measurement. If you want to stop using while the
vehicle is still in motion, be sure to turn off the velocity compensation using the Mode field in the Velocity
Compensation Control Register in the Velocity Ading subsystem.

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9.2

Configuration Registers

9.2.1

Velocity Compensation Control

Velocity Compensation Control
51
Access : Read / Write
Provides control over the velocity compensation feature for the attitude filter.
8
$VNRRG,51,1,0.1,0.01*5A
Format
Unit
Description
uint8
Selects the type of velocity compensation performed by
the VPE. See the table below for available options.
VelocityTuning
float
Tuning parameter for the velocity measurement.
RateTuning
float
Tuning parameter for the angular rate measurement.

Table 4 - Velocity Compensation Modes
Value
0
1

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Description
Disabled.
Body Measurement.

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9.3

Status Registers

9.3.1

Velocity Compensation Status

INTERNAL REGISTER
This register is not listed in the public User Manual. It is not recommended to supply this register to
customers unless there is a specific reason to do so.

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Velocity Compensation Status
52
Access : Read
Provides diagnostic status information for the velocity compensation algorithm.
8
$VNRRG,51,1,0.1,0.01*5A
Format
Unit
Description
float
m/s
Estimated velocity magnitude.
2
float
m/s
Estimated acceleration magnitude.
float[3]
m/s2
Estimated acceleration offset.
float[3]
rad/s
Filtered angular rate.

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9.4

Input Measurements

9.4.1

Velocity Compensation Measurement

Velocity Compensation Measurement
50
Access : Read / Write
Input register for a velocity measurement to be used by the filter to compensate for
acceleration disturbances.
12
$VNRRG,50,37.2,0,0*42
Format
Unit
Description
float
m/s
Velocity in the X-Axis measured in the sensor frame.
float
m/s
Velocity in the Y-Axis measured in the sensor frame.
float
m/s
Velocity in the Z-Axis measured in the sensor frame.

For Mode 1 (body measurement mode) the VN-100 will compute the vector length of the provided 3D
velocity vector and use this for velocity compensation. If you have a scalar measurement you can set
only the X-axis and set the Y & Z to zero.

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9.5

Factory Defaults

Settings Name
Velocity Compensation Control

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Default Factory Value
1,0.1,0.01

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document, and the products and services described herein at any time, without notice.

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their respective owners.

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