Aceinna IMU381 SERIES User manual

IMU381 Series User’s Manual
Doc# 7430-3881-02
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ACEINNA, Inc.
email: [e-mail], website: www.aceinna.com
IMU381 SERIES USER MANUAL
Document Part Number: 7430-3881-02

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Doc# 7430-3881-02

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Revision History
Date
Document
Revision
Firmware
Applicability
Description
Author(s)
Mar 12,
2018
Rev. 1.0
v19.1.x
Baseline release of IMU381
manual
Feng Liu
Feb 15,
2019
Rev. 2.0
•Update SPI functionality
•This document only describes
usage of the IMU381.
References to other products
have been removed
•Corrections and clarifications
•Removed references to
magnetometer, GPS, and
EKF algorithms, including
some Appendixes
John Newton
Joe Motyka
YiFan Li
David Garnett

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Table of Contents
1Introduction .............................................................................................................................. 1
Manual Overview .............................................................................................................. 1
Overview of the IMU381 Series Inertial Measurement Unit ............................................ 2
2Interface.................................................................................................................................... 3
Electrical Interface ............................................................................................................ 3
2.1.1 Connector and Mating Connector .............................................................................. 3
2.1.2 Power Input and Power Input Ground........................................................................4
2.1.3 Serial Data Interface................................................................................................... 4
2.1.4 Reserved – Factory Use Only..................................................................................... 5
Mechanical Interface ......................................................................................................... 5
3Theory of Operation ................................................................................................................. 6
IMU381 Series Default Coordinate System ...................................................................... 8
3.1.1 Advanced Settings...................................................................................................... 9
IMU381 Theory of Operation ........................................................................................... 9
3.2.1 IMU381 Advanced Settings....................................................................................... 9
3.2.2 IMU381 Built-In Test .............................................................................................. 10
4IMU381 SPI Port Interface Definition ................................................................................... 11
IMU381 Register Map..................................................................................................... 11
IMU381 SPI Register Read Methodology ...................................................................... 13
4.2.1 IMU381 SPI Port Polled-Mode Read....................................................................... 14
4.2.2 IMU381 SPI Port Burst-Mode Read ........................................................................ 15
Output Data Registers ..................................................................................................... 18
System Registers ............................................................................................................. 19
Diagnostic Status Register............................................................................................... 19
IMU381 SPI Register Write Methodology...................................................................... 20
Configuration Registers................................................................................................... 22
4.7.1 Self-Test/Data-Ready............................................................................................... 22
4.7.2 Output Data Rate...................................................................................................... 22
4.7.3 Rate-Sensor Scaling/Low-Pass Filter....................................................................... 23
4.7.4 Accelerometer, and Alternate Rate-Sensor Scaling ................................................. 25
4.7.5 Axis Orientation Settings ......................................................................................... 27
4.7.6 Saving the Configuration to EEPROM ....................................................................27
4.7.7 Hardware and Software Version .............................................................................. 27

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Suggested Operation........................................................................................................ 28
4.8.1 Startup Timing ......................................................................................................... 28
4.8.2 SPI Timing ............................................................................................................... 29
Signal Synchronization.................................................................................................... 30
Bootloader ....................................................................................................................... 31
5IMU381 UART Port Interface Definition .............................................................................. 32
General Settings .............................................................................................................. 32
Number Formats.............................................................................................................. 32
Packet Format.................................................................................................................. 33
5.3.1 Packet Header........................................................................................................... 33
5.3.2 Packet Type.............................................................................................................. 33
5.3.3 Payload Length......................................................................................................... 34
5.3.4 Payload..................................................................................................................... 34
5.3.5 16-bit CRC-CCITT .................................................................................................. 34
5.3.6 Messaging Overview................................................................................................ 34
6IMU381 Standard UART Port Commands and Messages ..................................................... 37
Link Test.......................................................................................................................... 37
6.1.1 Ping Command......................................................................................................... 37
6.1.2 Ping Response .......................................................................................................... 37
6.1.3 Echo Command........................................................................................................ 37
6.1.4 Echo Response ......................................................................................................... 37
Interactive Commands..................................................................................................... 37
6.2.1 Get Packet Request .................................................................................................. 38
6.2.9 Error Response......................................................................................................... 38
Output Packets (Polled)................................................................................................... 38
6.3.1 Identification Data Packet ........................................................................................ 38
6.3.2 Version Data Packet................................................................................................. 39
6.3.3 Test 0 (Detailed BIT and Status) Packet .................................................................. 39
Output Packets (Polled or Continuous) ........................................................................... 40
6.4.1 Scaled Sensor Data Packet 0 .................................................................................... 40
6.4.2 Scaled Sensor Data Packet 1 (Default IMU Data) ................................................... 41
7IMU381 Advanced UART Port Commands........................................................................... 43
Configuration Fields........................................................................................................ 43
Continuous Packet Type Field......................................................................................... 44

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Digital Filter Settings ...................................................................................................... 44
Orientation Field.............................................................................................................. 44
User Behavior Switches .................................................................................................. 46
Commands to Program Configuration............................................................................. 46
7.6.1 Write Fields Command ............................................................................................ 46
7.6.2 Set Fields Command ................................................................................................ 47
Read Fields Command .................................................................................................... 48
Read Fields Response...................................................................................................... 49
Get Fields Command....................................................................................................... 49
Get Fields Response ........................................................................................................ 50
8IMU381 Advanced UART Port BIT ...................................................................................... 51
Built In Test (BIT) and Status Fields .............................................................................. 51
Master BIT and Status (BITstatus) Field......................................................................... 53
hardwareBIT Field .......................................................................................................... 54
hardwarePowerBIT Field ................................................................................................ 54
hardwareEnvironmentalBIT Field................................................................................... 54
comBIT Field .................................................................................................................. 55
comSerialABIT Field ...................................................................................................... 55
comSerialBBIT Field ...................................................................................................... 55
softwareBIT Field............................................................................................................ 56
softwareAlgorithmBIT Field........................................................................................... 56
softwareDataBIT Field .................................................................................................... 56
hardwareStatus Field ....................................................................................................... 56
comStatus Field ............................................................................................................... 57
softwareStatus Field ........................................................................................................ 57
sensorStatus Field............................................................................................................ 57
Configuring the Master Status......................................................................................... 58
8.16.1 hardwareStatusEnable Field..................................................................................... 58
8.16.2 comStatusEnable Field............................................................................................. 58
8.16.3 softwareStatusEnable Field...................................................................................... 58
8.16.4 sensorStatusEnable Field ......................................................................................... 59
9IMU381 BOOTLOADER ...................................................................................................... 60
Updating firmware over UART Interface ....................................................................... 60
9.1.1 Jump to BootLoader Command ............................................................................... 60

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9.1.2 Write APP Command............................................................................................... 60
9.1.3 Jump to Application command ................................................................................ 61
Updating firmware using the SPI Interface..................................................................... 61
9.2.1 Boot Mode Registers................................................................................................ 61
9.2.2 Boot Mode Status Register (0x78) ........................................................................... 62
9.2.3 Boot Command Register (0x7A).............................................................................. 63
9.2.4 Boot Data Register (0x7C)....................................................................................... 64
9.2.5 Boot Loading Sequence ........................................................................................... 64
10 Warranty and Support Information ..................................................................................... 66
10.3.1 Authorization............................................................................................................ 66
10.3.2 Identification and Protection .................................................................................... 66
10.3.3 Sealing the Container ............................................................................................... 67
10.3.4 Marking.................................................................................................................... 67
Appendix A: Installation and Operation of NAV-VIEW .............................................................. 68
NAV-VIEW Computer Requirements ....................................................................................... 68
Install NAV-VIEW ................................................................................................................. 68
Connections................................................................................................................................ 68
Setting up NAV-VIEW .............................................................................................................. 68
Data Recording........................................................................................................................... 69
Data Playback............................................................................................................................. 70
Raw Data Console...................................................................................................................... 70
Horizon and Compass View....................................................................................................... 71
Packet Statistics View ................................................................................................................ 72
Unit Configuration ..................................................................................................................... 72
Advanced Configuration ............................................................................................................ 73
Bit Configuration........................................................................................................................ 74
Read Unit Configuration ............................................................................................................ 76
Appendix B: Sample Packet-Parser Code...................................................................................... 80
Overview .................................................................................................................................... 80
Code listing ................................................................................................................................ 81
Appendix C: Sample Packet Decoding.......................................................................................... 88

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About this Manual
The following symbols are used to provide additional information.
NOTE
Note provides additional information about the topic.
EXAMPLE
This symbol indicates an example that will help the reader understand the terminology.
IMPORTANT
This symbol defines items that have significant meaning to the user
WARNING
The user should pay particular attention to this symbol. It means there is a chance that physical
harm could happen to either the person or the equipment.
This manual uses the following paragraph heading formats:
1 Heading 1
1.1 Heading 2
1.1.1 Heading 3
1.1.1.1 Heading 4
Normal

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1Introduction
Manual Overview
This manual describes ACEINNA’s IMU381 IMU Inertial Measurement Unit. The IMU381 will
be referred to as “the unit” frequently in this document.
For users wishing to get started quickly, please refer to the two-page quick start guide included
with each evaluation kit shipment. Table 1 highlights the content in each section and suggests
how to use this manual.
Table 1 Manual Content
Manual Section Who Should Read?
Section 1:
Manual Overview
All customers should read sections 1.1 and 1.2.
Section 2:
Interface
Customers designing the electrical and mechanical interface to the IMU381
series products should read Section 2.
Section 3:
Theory of Operation
All customers should read Section 3.
Section 4:
SPI Port Interface
Customers designing the software interface to the IMU381 series products
SPI Port should review Section 4.
Section 5-8:
UART Port Interface
Customers designing the software interface to the IMU381 series products
UART Port should review Sections 5-8.
Section 9:
IMU381 Bootloader
Customers that intend to update Aceinna firmware in the unit should read
this section
Section 10:
Warranty and Support Information
All customers should read Section 10.
Appendix A:
Installation and Operation of NAV-
VIEW
All customers should read Appendix A.
Appendix B:
Sample Packet-Parser Code
All customers that intend to create scripts to interface with serial messages
should read Appendix B
Appendix C:
Sample Packet Decoding
All customers that intend to create scripts to interface with serial messages
should read Appendix C

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Overview of the IMU381 Series Inertial Measurement Unit
This manual describes the use of ACEINNA’s IMU381 and is intended to be used as a detailed
technical reference and operating guide. ACEINNA’s IMU381 Series products combine the latest
in high-performance commercial MEMS (Micro-electromechanical Systems) sensors and digital
signal processing techniques to provide a small, cost-effective alternative to existing IMU
systems.
The IMU381 Series is ACEINNA’s fourth generation of MEMS-based Inertial Systems, building
on over a decade of field experience, and encompassing thousands of deployed units and millions
of operational hours in a wide range of land, marine, airborne, and instrumentation applications.
It is designed for OEM applications.
At the core of the IMU381 Series is a rugged 6-DOF (Degrees of Freedom) MEMS inertial sensor
cluster. The 6-DOF MEMS inertial sensor cluster includes three axes of MEMS angular rate
sensing and three axes of MEMS linear acceleration sensing. These sensors are based on rugged,
field proven silicon bulk micromachining technology. Each sensor within the cluster is
individually factory calibrated for temperature and non-linearity effects during ACEINNA’s
manufacturing and test process using automated thermal chambers and rate tables.
Another unique feature of the IMU381 Series is the extensive field configurability of the units.
This field configurability allows the IMU381 Series of Inertial Systems to satisfy a wide range of
applications and performance requirements with a single mass produced hardware platform. The
basic configurability includes parameters such as baud rate (UART), clock speed (SPI), packet
type, and update rate, and the advanced configurability includes the defining of custom axes.
The IMU381 Series module is packaged in a lightweight, rugged, unsealed metal enclosure that is
designed for cost-sensitive commercial and OEM applications. The unit can be configured to
output data over a SPI Port or a low level UART serial port. The port choice is user controlled by
grounding the appropriate pin on the connector. ACEINNA’s NAV-VIEW 3.X Windows
application supports using the unit low level UART data port NAV-VIEW 3.X is a powerful
Windows-based operating tool that provides complete field configuration, diagnostics, charting of
sensor performance, and data logging with playback.

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2Interface
Electrical Interface
2.1.1 Connector and Mating Connector
The unit main connector is a SAMTEC FTM-110-02-F-DV-P defined in Figure 1. The SAMTEC
CLM-110-02 mating connector is compatible with the IMU381unit main connector.
Figure 1 IMU381 Interface Connector
Table 2 Interface Connector Pin Definition IMU381 vs. IMU380 (Previous Generation)
Pin Pin Description- IMUx80I0 (For Reference) Pin Description (IMU381I3)
1
Reserved – factory use only
Inertial-Sensor Sampling Indicator (sampling
upon falling edge)
2
Synchronization Input (1 kHz Pulse used to
synchronize SPI Comm)
Synchronization Input (1 kHz Pulse used to
synchronize SPI Comm). If used, this clock
should be 1kHz +/- 0.1%
3
SPI Clock (SCLK) / UART TX
SPI Clock (SCLK) / UART TX
4
SPI Data Output (MISO) / UART RX
SPI Data Output (MISO) / UART RX
5
SPI Data Input (MOSI)
SPI Data Input (MOSI)
6
SPI Chip Select (SS)
SPI Chip Select (SS)

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2.1.2 Power Input and Power Input Ground
Power is applied to the unit on pins 10 through 15. Pins 13-15 are ground; Pins 10-12 accepts 3
to 5 VDC unregulated input. Note that these are redundant power ground input pairs.
WARNING
Do not reverse the power leads or damage may occur. Do not add greater than 5.5 volts on the
power pins or damage may occur. This system has no reverse voltage or over-voltage protection.
2.1.3 Serial Data Interface
The user can select the serial interface used with the unit by controlling the logic level on
connector pin 7 at system startup. If pin 7 is left floating then the unit is configured for SPI
communications on pins 3-6. Pin 7 is set as an output and used as the DATA READY discrete
for SPI communications. Additionally, the user can synchronize the output data on the SPI port
by providing a 1 kHz input pulse on Pin 2. For the complete SPI interface definition, please refer
to Section 4.
If the connector pin 7 is grounded then the unit is configured for low-level UART output on pins
3 and 4. This is a standard UART asynchronous output data port. For the complete UART
interface definition, please refer to Sections 5-0. Note that the two output port interface methods
7
Data Ready (SPI Communication Data Ready) /
SPI-UART Port Select
Data Ready (SPI Communication Data Ready) /
SPI-UART Port Select
8
External Reset (NRST)
External Reset (NRST)
9
Reserved – factory use only
Reserved – factory use only
10
Power VIN (3-5 VDC)
Power VIN (3-5 VDC)
11
Power VIN (3-5 VDC)
Power VIN (3-5 VDC)
12
Power VIN (3-5 VDC)
Power VIN (3-5 VDC)
13
Power GND
Power GND
14
Power GND
Power GND
15
Power GND
Power GND
16
Reserved – factory use only
Reserved – factory use only
17
Reserved
Reserved
18
Reserved – factory use only
Reserved – factory use only
19
Reserved
Reserved
20
Reserved – factory use only
Reserved – factory use only

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are controlled independently from each other. The UART port output controls apply only to data
being output over the UART port, and the SPI output controls apply only to data being output
over the SPI port.
2.1.3.1 SPI Com Synchronization Input
Pin 2 can be used as a sync pulse to force synchronization of sensor data collection to a 1 kHz
rising-edge signal for output over the SPI port. See Section 4.9 for a more complete description.
2.1.4 Reserved – Factory Use Only
During normal operation of the unit no connection is made to the Reserved – factory use only
pins. These pins have internal pull-up mechanisms and must have no connections for the unit to
operate properly.
Mechanical Interface
The IMU381 mechanical interface is defined by the outline drawing in Figure 2.
Figure 2 IMU381 Outline Drawing
NOTES UNLESS OTHERWISE STATED:
1) MATING CONNECTOR SAMTEC CLM-110-02
2) DIMENSION TO CENTROID OF PIN ONE

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3Theory of Operation
This section of the manual covers detailed theory of operation for the IMU381
Figure 3 shows the IMU381 Series hardware block diagram. At the core of the IMU381 Series is
a rugged 6-DOF (Degrees of Freedom) MEMS inertial sensor cluster. The 6-DOF MEMS inertial
sensor cluster includes three axes of MEMS angular rate sensing and three axes of MEMS linear
acceleration sensing. These sensors are based on rugged, field proven silicon bulk
micromachining technology. Each sensor within the cluster is individually factory calibrated
using ACEINNA’s automated manufacturing process. Sensor errors are compensated for
temperature bias, scale factor, non-linearity and misalignment effects using a proprietary
algorithm from data collected during manufacturing. Accelerometer and rate gyro sensor bias
shifts over temperature (-40 0C to +71 0C) are compensated and verified using calibrated thermal
chambers and rate tables.
The 6-DOF inertial sensor cluster data is fed into a high speed signal processing chain, which
provides the sensor compensation and digital filtering. Measurement data packets are available at
fixed continuous output rates or on a polled basis from the SPI port or the UART port. The SPI
port outputs data via registers, and the user can perform polled reads of each register, or a block
burst read of a set of predefined registers. Output data over the SPI port can be synchronized to
an external 1 kHz pulse. The complete SPI interface is defined in Section 5. The UART port
outputs data packets are asynchronous and defined in Sections 6-8.
Sensors
High-Speed
Sampling
+
Sensor
Compensation, Calibration
and Filtering
X/Y/Z
Gyros
X/Y/Z
Accelerometers
Temperature
Sensor
UART1
SPI
SPI Register Read/Write
• X/Y/Z Acceleration
• X/Y/Z Angular Rate
ACEINNA Serial Protocol
• X/Y/Z Acceleration
• X/Y/Z Angular Rate
1KHz Pulse
(+/- 0.01Hz)
Processor
Figure 3 IMU381 Series Hardware Block Diagram
Figure 4 shows the software block diagram. The 6-DOF inertial sensor cluster data is fed into a
high speed 200Hz signal processing chain. These 6-DOF signals pass through one or more of the

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processing blocks and these signals are converted into output measurement data as shown.
Measurement data packets are available at fixed continuous output rates or on a polled basis.
As shown in the software block diagram, the IMU381 Series has a unit setting and profile block
which configures the algorithm to user and application specific needs. This feature is one of the
more powerful features in the IMU381 Series architecture as it allows the IMU381 Series to work
in a wide range of commercial applications by settings different modes of operation for the
IMU381 Series.
6-DOF Sensor Cluster
X/Y/Z Body
Angular Rates
Unit Settings & Profile
• Communication Settings
• Axes Orientation
• Low Pass Filter
• Programmable BIT Alerts
X/Y/Z Body
Accelerations
Measurement Data
Available to User
(Fixed Rate or Polled)
IMU Scaled Packets
(S0, S1)
200Hz
Sensor Processing
Sensor
Filtering
User Outputs
User Inputs
Sensor Inputs
Processing
Built-In Test &
Status Data
Status
Packet
(T0)
Sensor
Calibration
Axes Rotation
Figure 4 IMU381 Series Software Block Diagram

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IMU381 Series Default Coordinate System
The IMU381 Series Inertial System default coordinate systems are shown in Figure 6. As with
many elements of the IMU381 Series, the coordinate system is configurable with either NAV-
VIEW or by sending the appropriate serial commands over the UART port. These configurable
elements are known as Advanced Settings. This section of the manual describes the default
coordinate system settings of the IMU381 Series when it leaves the factory.
Figure 5 IMU381 Default Coordinate Frame
The axes form an orthogonal SAE right-handed coordinate system. Acceleration is positive when
it is oriented towards the positive side of the coordinate axis. For example, with a IMU381 Series
product sitting on a level table, it will measure zero g along the x- and y-axes and -1 g along the
z-axis. Normal Force acceleration is directed upward, and thus will be defined as negative for the
IMU381 Series z-axis.
The angular rate sensors are aligned with these same axes. The rate sensors measure angular
rotation rate around a given axis. The rate measurements are labeled by the appropriate axis. The
direction of a positive rotation is defined by the right-hand rule. With the thumb of your right
hand pointing along the axis in a positive direction, your fingers curl around in the positive
rotation direction. For example, if the IMU381 Series product is sitting on a level surface and you
rotate it clockwise on that surface, this will be a positive rotation around the z-axis. The x- and y-
axis rate sensors would measure zero angular rates, and the z-axis sensor would measure a
positive angular rate.

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3.1.1 Advanced Settings
The IMU381 Series Inertial Navigation Units have a number of advanced settings that can be
changed. All units support baud rate1, power-up output packet type, output rate, sensor low pass
filtering, and custom axes configuration. The units can be configured using NAV-VIEW, as
described in Appendix A, and also directly with serial commands as described in Sections 5-8.
IMU381 Theory of Operation
The unit provides inertial rate and acceleration data in 6-DOF (six degrees of freedom). The unit
signal processing chain consists of the 6-DOF sensor cluster, programmable low-pass filters, and
a signal processing component for sensor error compensation. The unit has a UART input/output
port and a SPI input/output port.
After passing through a digitally controlled programmable low-pass filter, the rate and
acceleration sensor signals are obtained at 200Hz.. The factory calibration data, stored in
EEPROM, is used by the processor to remove temperature bias, misalignment, scale factor errors,
and non-linearities from the sensor data. Additionally any advanced user settings such as axes
rotation are applied to the IMU data. The 200Hz IMU data is continuously being maintained
inside the unit, and is available at 200Hz on the SPI output port registers. Digital IMU data is
output over the UART port at a selectable fixed rate (100, 50, 25, 20, 10, 5 or 2 Hz) or on as-
requested basis using the GP, ‘Get Packet’ command. The digital IMU data is available in
several measurement packet formats including Scaled Sensor Data (‘S1’ Packet). In the Scaled
Sensor Data (‘S1’ Packet), data is output in scaled engineering units. See Section 6 of the manual
for full packet descriptions.
3.2.1 IMU381 Advanced Settings
The unit advanced settings are described in Table 6. All of the advanced settings are accessible
through NAV-VIEW under the Configuration Menu, Unit Configuration settings. For a full
definition of the SPI port please see section 4.
Table 6 IMU381 Advanced Settings
Setting Default Comments
Baud Rate 38,400 baud 57600, 115200, and 230400 also available
Packet Type
S0 S1 also available
Packet Rate
100Hz
This setting sets the rate at which selected Packet Type, packets are output. If
polled mode is desired, then select Quiet. If Quiet is selected, the unit will only
send measurement packets in response to GP commands.
Orientation See Figure 6. To configure the axis orientation, select the desired measurement for each
axis: NAV-VIEW will show the corresponding image of the unit, so it easy to
visualize the mode of operation. Refer to Section 7.4 Orientation Field settings
for the twenty four possible orientation settings.
1Note: certain combinations of baud-rate, packet-type, and output data rate are invalid because the time to transmit the data exceeds a
limit on the permissible message length. The IMU381 limits the output packet width to 80% of the time between data packets. For
instance, if the packet is output every 10 milliseconds (100 Hz) then the packet width must be less than 8 milliseconds or the
combination is not allowed. This prevents messages from overlapping and causing communication problems. For this reason, 57.6
kbps and higher baud-rates are suggested.

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Setting
Default
Comments
Filter Settings
(unfiltered, 2, 5,
10, 20, 25, 40 50
Hz).
20 Hz The low pass filters are set to a default of 20 Hz for the accelerometers, and 20
Hz for the angular rate sensors. There is one filter setting for all three angular
rate sensors. There is one filter setting for all three accelerometers. Setting
either to zero disables the low-pass filter.
BIT
See section 8.1
NOTE on Filter Settings
Generally, there is no reason to change the low-pass filter settings on the unit or other IMU381
Series Inertial Systems. However, when a IMU381 Series product is installed in an environment
with a lot of vibration, it can be helpful to reduce the vibration-based signal energy and noise
prior to further processing on the signal. Installing the unit in the target environment and
reviewing the data with NAV-VIEW can be helpful to determine if changing the filter settings
would be helpful. Although the filter settings can be helpful in reducing vibration based noise in
the signal, low filter settings (e.g., 5Hz) also reduce the bandwidth of the signal, which can wash
out the signals containing the dynamics of a target. Therefore, caution should be used when
changing the filter settings.
3.2.2 IMU381 Built-In Test
The unit Built-In Test capability allows users of the unit to monitor health, diagnostic, and system
status information of the unit in real-time. The Built-In Test information consists of a BIT word
(2 bytes) transmitted in every measurement packet. In addition, there is a diagnostic packet ‘T0’
that can be requested via the Get Packet ‘GP’ command which contains a complete set of status
for each hardware and software subsystem in the unit. See Sections 5-0 for details on the ‘T0’
packet.
The BIT word, which is contained within each measurement packet, is detailed below. The LSB
(Least Significant Bit) is the Error byte, and the MSB (Most Significant Bit) is a Status byte with
programmable alerts. Internal health and status are monitored and communicated in both
hardware and software. The ultimate indication of a fatal problem is the masterFail flag.
The masterStatus flag is a configurable indication that can be modified by the user. This flag is
asserted as a result of any asserted alert signals which have been enabled. See Advanced BIT
(Section 8) for details regarding the configuration of the masterStatus flags. Table 7 shows the
BIT definition and default settings for BIT programmable alerts in the unit.
Table 7 IMU381 Default BIT Status Definition
BITstatus Field
Bits
Meaning
Category
masterFail
0
0 = normal, 1 = fatal error has occurred
BIT
HardwareError
1
0 = normal, 1= internal hardware error
BIT
comError 2 0 = normal, 1 = communication error BIT
softwareError 3 0 = normal, 1 = internal software error BIT
Reserved 4:7 N/A N/A
masterStatus
8
0 = nominal, 1 = Alert, Sensor Over Range
Status
hardwareStatus
9
Disabled
Status
comStatus
10
Disabled
Status
softwareStatus 11 Disabled Status
sensorStatus 12 0 = nominal, 1 = Sensor Over Range Status

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BITstatus Field
Bits
Meaning
Category
Reserved 13:15 N/A N/A
The unit also allows a user to configure the Status byte within the BIT message. To configure the
word, select the BIT Configuration tab from the Unit Configuration menu. The dialog box allows
selection of which status types to enable (hardware, software, sensor, and comm). In the case of
the unit, which has fewer features and options than other Acienna measurement products, the only
meaningful parameter is sensor over-range. It is recommended that users leave the default
configuration, which is sensorStatus enabled and flag on sensor over-range. The over-range only
applies to the rotational rate sensors. Because instantaneous acceleration levels due to vibration
can exceed the accelerometer sensor range in many applications, none of the IMU381 Series
products trigger over-range on accelerometer readings.
4IMU381 SPI Port Interface Definition
The IMU381 provides a SPI interface for data communications. This section of the user’s manual
defines the unit register map, register control capabilities, and the data register reading and
writing methodologies.
The unit operates as a slave device. The master device must be configured to communicate with
the unit using the following settings:
•Data transferred in 16-bit word-length and MSB-first
•fCLK ≤ 2.0 MHz
•CPOL = 1 (clock polarity) and CPHA = 1 (clock phase)
Additional operational requirements are described in Section 4.8.
IMU381 Register Map
Table 3 describes the IMU381 register map. In the following tables the phrasing “<address1> to
<address2>” means all addresses in the inclusive range from <address1> through <address2> and
the phrasing “<read-address>/<write-address>” means that the register is read from the <read-
address> and written to the <write-address>.
NOTE: Sensor data scaling is specific to the message or register being read.
Please see scaling information for each sensor data read operation. Specifically,
the sensor data in the SPI S0_BURST, the SPI S1_BURST, the UART S0 message
and the UART S1 message are scaled differently than the scaling for reading the
individual SPI sensor data registers.
Table 3 IMU381 Register Map2
Name
Read/Write
Address
Default
Function
Reserved
N/A
0x00 to 0x03
N/A
N/A
X_RATE
R
0x04
N/A
X-Axis Rate-Sensor Output
2Register and data-packet availability is based on the features of the DMU381ZA..

IMU381 Series User’s Manual
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Doc# 7430-3881-02 Page 12
Name
Read/Write
Address
Default
Function
Y_RATE
R
0x06
Y-Axis Rate-Sensor Output
Z_RATE
R
0x08
Z-Axis Rate-Sensor Output
X_ACCEL
R
0x0A
N/A
X-Axis Accelerometer Output
Y_ACCEL
R
0x0C
Y-Axis Accelerometer Output
Z_ACCEL
R
0x0E
Z-Axis Accelerometer Output
Reserved
N/A
0x10 to 0x15
N/A
RATE_TEMP
R
0x16
N/A
Rate-sensor temperature
BOARD_TEMP
R
0x18
N/A
Board temperature
TIMESTAMP1
R
N/A
N/A
Time in µs from sensor sampling to active edge of 1kHz
synch clock. Only available as part of extended burst data
packet
TIMESTAMP2
R
N/A
N/A
Time in µs from active edge of 1kHz synch clock to data
ready signal. Only available as part of extended burst data
packet
Reserved
R
0x1A to 0x33
N/A
SELF_TEST
3
R/W
0x34/0x35
0x00
Initiate Self-Test / Configure Data-Ready output signal
DATA_READY
R/W
0x35/0x34
0x04
OUTPUT_DATA_RATE
R/W
0x36/0x37
0x01
Table 12: Set Output Data Rate (ODR)
Reserved
N/A
0x37/0x36
0x01
RS_DYNAMIC_RANGE
R/W
0x38/0x39
0x02
See
Table 13: Set rate-sensor dynamic range (SPI only) /
Select digital filter
LOW_PASS_FILTER
R/W
0x39/0x38
0x06
Reserved
N/A
0x3A to 0x3B
N/A
STATUS
R
0x3C
N/A
See Table 9: Diagnostic register
STNDRD_BURST
R
0x3E
N/A
Command to perform a burst-read of the standard data-
packet
EXTNDED_BURST
R
0x3F
N/A
Command to perform a burst read of the extended data
packet
Reserved
R
0x3F to 0x40
S0_BURST
R
0x41
N/A
Burst-Mode Command for UCB scaled-sensor 0 data-
packet (see Section 6.4.1)
S1_
BURST
R
0x42
N/A
Burst-Mode Command for UCB scaled-sensor 1 data-
packet (see Section 6.4.2)
Reserved
N/A
0x43 to 0x51
N/A
MANUF_CODE
R
0x52
0x1310
Manufacturing code indicating year and location
UNIT_CODE
R
0x54
0x0000
Unit information code
3Register reads are performed 2-bytes at a time while writes are a single byte in length. In operation, the
SELF_TEST/DATA_READY register should be read together starting at register 0x34. This applies to other shared registers as well.