Table of Contents
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LP-BUS Protocol
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Each packet sent during the communication is based on the following structure:
Byte # | Name | Description |
0 | Packet start (3Ah) | Data packet start |
1 | OpenMATID byte 1 | Contains the low byte of the OpenMAT ID of the sensor to be communicated with. The default value of this ID is 1. The host sends out a GET / SET request to a specific LPMS sensor by using this ID, and the client answers to request also with the same ID. This ID can be adjusted by sending a SET command to the sensor firmware. |
2 | OpenMAT ID byte 2 | High byte of the OpenMAT ID of the sensor. |
3 | Command # byte 1 | Contains the low byte of the command to be performed by the data transmission. |
4 | Command # byte 2 | High byte of the command number. |
5 | Packet data length byte 1 | Contains the low byte of the packet data length to be transmitted in the packet data field. |
6 | Packet data length byte 2 | High byte of the data length to be transmitted. |
x | Packet data(n bytes) | If data length n not equal to zero, x = 6+1, 6+2…6+n. Otherwise x = none. This data field contains the packet data to be transferred with the transmission if the data length not equals to zero, otherwise the data field is empty. |
7+n | LRC byte 1 | The low byte of LRC checksum. To ensure the integrity of the transmitted data the LRC checksum is used. It is calculated in the following way: LRC = sum(OpenMAT ID, Command, Package data length, and packet data byte no. 1 to no. x) The calculated LRC is usually compared with the LRC transmitted from the remote device. If the two LRCs are not equal, and error is reported. |
8+n | LRC byte 2 | High byte of LRC check-sum. |
9+n | Termination byte 1 | 0Dh |
10+n | Termination byte 2 | 0Ah |
Data Format in a Packet Data Field
Generally, data is sent in little-endian format, low order byte first, high order byte last. Data in the data fields of a packet can be encoded in several ways, depending on the type of information to be transmitted. In the following we list the most common data types. Other command-specific data types are explained in the command reference.
Identifier | Description |
Int32 | 32-bit signed integer value |
Int16 | 16-bit signed integer value |
Float32 | 32-bit float value |
Vector3f | 3 element 32-bit float vector |
Vector3i16 | 3 element 16-bit signed integer vector |
Vector4f | 4 element 32-bit float vector |
Vector4i16 | 4 element 16-bit signed integer vector |
Matrix3x3f | 3x3 element float value matrix |
Sensor Measurement Data in Streaming Mode
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In 32-bit float transmission mode:
Chunk # | Data type | Sensor data |
1 | Float32 | Timestamp (ms) |
2 | Vector3f | Raw (uncalibrated) gyroscope data (deg/s) |
3 | Vector3f | Raw (uncalibrated) accelerometer data (g) |
4 | Vector3f | Raw (uncalibrated) magnetometer data (T) |
5 | Vector3f | Angular velocity (rad/s) |
6 | Vector4f | Orientation quaternion (normalized) |
7 | Vector3f | Euler angle data (rad) |
8 | Vector3f | Linear acceleration data (m/s2) |
9 | Float32 | Barometric pressure (mPa) |
10 | Float32 | Altitude (m) |
11 | Float32 | Temperature (°C) |
12 | Float32 | Heave motion (m) (optional) |
In 16-bit transmission mode values are transmitted to the host with a multiplication factor applied to increase precision:
Order # | Data type | Sensor data | Factor |
1 | uint32 | Timestamp (s) | 400 |
2 | Vector3i16 | Raw (uncalibrated) gyroscope data (rad/s) | 1000 |
3 | Vector3i16 | Raw (uncalibrated) accelerometer data (g) | 1000 |
4 | Vector3i16 | Raw (uncalibrated) magnetometer data (uT) | 100 |
5 | Vector3i16 | Angular velocity (rad/s) | 1000 |
6 | Vector4i16 | Orientation quaternion (normalized) | 10000 |
7 | Vector3i16 | Euler angle data (rad) | 10000 |
8 | Vector3i16 | Linear acceleration data (g) | 1000 |
9 | Int16 | Barometric pressure (kPa) | 100 |
10 | Int16 | Altitude (m) | 10 |
11 | Int16 | Temperature (°C) | 100 |
12 | Int16 | Heave motion (m) (optional) | 1000 |
NOTE: Raw accelerometer data is transmitted with misalignment correction and scaling to g units applied. Raw gyroscope data is transmitted with misalignment correction, bias correction and scaling to rad/s applied. Raw magnetometer data is transmitted with misalignment correction and scaling to uT applied, hard and soft iron calibration is not applied to raw magnetometer data transmitted directly from sensor.
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GET request (HOST -> SENSOR)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT ID MSB |
3 | 04h | Command no. LSB (4d = GET_CONFIG) |
4 | 00h | Command no. MSB |
5 | 00h | Data length LSB (GET command = no data) |
6 | 00h | Data length MSB |
7 | 05h | Check sum LSB |
8 | 00h | Check sum MSB |
9 | 0Dh | Packet end 1 |
10 | 0Ah | Packet end 2 |
Reply data (SENSOR -> HOST)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT LSB (ID = 1) |
2 | 00h | OpenMAT MSB |
3 | 04h | Command no. LSB (4d = GET_CONFIG) |
4 | 00h | Command no. MSB |
5 | 04h | Data length LSB (32-bit integer = 4 bytes) |
6 | 00h | Data length MSB |
7 | xxh | Configuration data byte 1 (LSB) |
8 | xxh | Configuration data byte 2 |
9 | xxh | Configuration data byte 3 |
10 | xxh | Configuration data byte 4 (MSB) |
11 | xxh | Check sum LSB |
12 | xxh | Check sum MSB |
13 | 0Dh | Packet end 1 |
14 | 0Ah | Packet end 2 |
xx = Value depends on the current sensor configuration.
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GET request (HOST -> SENSOR)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT ID MSB |
3 | 1Ah | Command no. LSB (26d = GET_GYR_RANGE) |
4 | 00h | Command no. MSB |
5 | 00h | Data length LSB (GET command = no data) |
6 | 00h | Data length MSB |
7 | 1Bh | Check sum LSB |
8 | 00h | Check sum MSB |
9 | 0Dh | Packet end 1 |
10 | 0Ah | Packet end 2 |
Reply data (SENSOR -> HOST)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT ID MSB |
3 | 1Ah | Command no. LSB (26d = GET_GYR_RANGE) |
4 | 00h | Command no. MSB |
5 | 04h | Data length LSB (32-bit integer = 4 bytes) |
6 | 00h | Data length MSB |
7 | xxh | Range data byte 1 (LSB) |
8 | xxh | Range data byte 2 |
9 | xxh | Range data byte 3 |
10 | xxh | Range data byte 4 (MSB) |
11 | xxh | Check sum LSB |
12 | xxh | Check sum MSB |
13 | 0Dh | Packet end 1 |
14 | 0Ah | Packet end 2 |
xx = Value depends on the current sensor configuration.
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SET request (HOST -> SENSOR)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT ID MSB |
3 | 1Fh | Command no. LSB (31d = SET_ACC_RANGE) |
4 | 00h | Command no. MSB |
5 | 04h | Data length LSB (32-bit integer = 4 bytes) |
6 | 00h | Data length MSB |
7 | 08h | Range data byte 1 (Range indicator 8g = 8d) |
8 | 00h | Range data byte 2 |
9 | 00h | Range data byte 3 |
10 | 00h | Range data byte 4 |
11 | 2Bh | Check sum LSB |
12 | 00h | Check sum MSB |
13 | 0Dh | Packet end 1 |
14 | 0Ah | Packet end 2 |
Reply data (SENSOR -> HOST)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT ID MSB |
3 | 00h | Command no. LSB (0d = REPLY_ACK) |
4 | 00h | Command no. MSB |
5 | 00h | Data length LSB (ACK reply = no data) |
6 | 00h | Data length MSB |
11 | 01h | Check sum LSB |
12 | 00h | Check sum MSB |
13 | 0Dh | Packet end 1 |
14 | 0Ah | Packet end 2 |
Read Sensor Data
Get request (HOST -> SENSOR)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT MSB |
3 | 09h | Command no. LSB (9d = GET_SENSOR_DATA) |
4 | 00h | Command no. MSB |
5 | 00h | Data length LSB (GET command = no data) |
6 | 00h | Data length MSB |
7 | 0Ah | Check sum LSB |
8 | 00h | Check sum MSB |
9 | 0Dh | Packet end 1 |
10 | 0Ah | Packet end 2 |
Reply data (SENSOR -> HOST)
Packet byte no. | Content | Meaning |
0 | 3Ah | Packet start |
1 | 01h | OpenMAT ID LSB (ID = 1) |
2 | 00h | OpenMAT ID MSB |
3 | 09h | Command no. LSB (9d = GET_SENSOR_DATA) |
4 | 00h | Command no. MSB |
5 | 34h | Data length LSB (56 bytes) |
6 | 00h | Data length MSB |
7-10 | xxxxxxxxh | Timestamp |
11-14 | xxxxxxxxh | Gyroscope data x-axis |
15-18 | xxxxxxxxh | Gyroscope data y-axis |
19-22 | xxxxxxxxh | Gyroscope data z-axis |
23-26 | xxxxxxxxh | Accelerometer x-axis |
27-30 | xxxxxxxxh | Accelerometer y-axis |
31-34 | xxxxxxxxh | Accelerometer z-axis |
35-38 | xxxxxxxxh | Magnetometer x-axis |
39-42 | xxxxxxxxh | Magnetometer y-axis |
43-46 | xxxxxxxxh | Magnetometer z-axis |
47-50 | xxxxxxxxh | Orientation quaternion q0 |
51-54 | xxxxxxxxh | Orientation quaternion q1 |
55-58 | xxxxxxxxh | Orientation quaternion q2 |
59-62 | xxxxxxxxh | Orientation quaternion q3 |
63 | xxh | Check sum LSB |
64 | xxh | Check sum MSB |
65 | 0Dh | Message end byte 1 |
66 | 0Ah | Message end byte 2 |
xx = Value depends on the current configuration and measurement value.
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In ASCII output mode sensor data is transmitted as plain ASCII numerical text. The output format for each number is generally 16-bit integer, but with a multiplication factor applied to increase precision. The following multiplication factors are used:
Chunk # | Data type | Sensor data | Factor |
1 | uint32 | Timestamp (s) | 10000 |
2 | Vector3i16 | Raw ( |
bias calibrated) gyroscope data ( |
dps) | 1000 | ||
3 | Vector3i16 | Raw (uncalibrated) accelerometer data (g) | 1000 |
4 | Vector3i16 | Raw (uncalibrated) magnetometer data ( |
uT) | 1000 | |
5 | Vector3i16 | Angular velocity ( |
dps) | 1000 | ||
6 | Vector4i16 | Orientation quaternion (normalized) | 100000 |
7 | Vector3i16 | Euler angle data ( |
deg) | 1000 | ||
8 | Vector3i16 | Linear acceleration data (g) | 1000 |
9 | Int16 | Barometric pressure (kPa) | 1000 |
10 | Int16 | Altitude (m) | 10 |
11 | Int16 | Temperature (°C) | 100 |
12 | Int16 | Heave motion (m) (optional) | 1000 |
LP-CAN Protocol
To exchange data with LPMS through the CAN Bus interface, the serial LP-BUS protocol is split into CAN bus messages. We call this CAN bus wrapper for the LP-BUS protocol: LP-CAN.
A regular LP-CAN message is structured as shown below:
11-bit CAN identifier | The CAN identifier of a CAN message. This identifier is set to the value 514h+OpenMAT ID of target sensor for all LP-CAN transmissions. |
8 data bytes | Contains the actual data to be transmitted in a CAN message. |
An example packet with 4 data bytes wrapping from LP-BUS to LP-CAN results in the following CAN messages:
CAN Message #1:
Byte # | Name | Description |
0 | Packet start (3Ah) | Mark of the beginning of a data packet. |
1 | OpenMATID - byte 1 | Contains the low byte of the OpenMAT ID of the sensor to be communicated with. The default value of this ID is 1. The host sends out a GET / SET request to a specific sensor by using this ID, and the client answers to request alsowith the same ID. This ID can be adjusted by sending a SET command to the sensor firmware. |
2 | OpenMAT ID - byte 2 | High byte of the OpenMAT ID of the sensor |
3 | Command no. - byte 1 | Contains the low byte of the command to be performed by the data transmission |
4 | Command no. - byte 2 | High byte of the command number |
5 | Packet data length - byte 1 | Contains the low byte of the packet data length to be transmitted in the packet data field (in this example 4) |
6 | Packet data length - byte 2 | High byte of the data length to be transmitted (in this example 0) |
7 | Packet data | Packet data byte 0 |
CAN Message #2:
Byte # | Name | Description |
0 | Packet data | Packet data byte 1 |
1 | Packet data | Packet data byte 2 |
2 | Packet data | Packet data byte 3 |
3 | LRC byte 1 | The low byte of LRC check-sum. |
4 | LRC byte 2 | High byte of LRC check-sum. |
5 | Termination byte 1 | 0Dh |
6 | Termination byte 2 | 0Ah |
7 | Not used | 0 |
The number of messages needed to contain the data depends on the length of the data to be transmitted. Each CAN message is 8 bytes long. Unused bytes of a message are filled with 0.
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Therefore, using these parameters the following message formats can be adjusted:
Parameter settings | Resulting channel message setup | ||||||||
Channel mode = Sequential Value mode = 16-bit fixed point (signed) StartID = 514h IMU ID = 1 | CAN message #1:
CAN message #2:
CAN message #3:
CAN message #4:
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Channel mode = Sequential Value mode = 32-bit floating point Start ID = 514h IMU ID = 1 | CAN message #1:
CAN message #2:
CAN message #3:
CAN message #4:
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Channel mode = CANopen Value mode = 16-bit fixed point (signed) Start ID = 180h IMU ID = 1 | CAN message |
#1:
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CAN message #6:
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CAN message |
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CAN message |
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Channel mode = CANopen
Value mode = 16-bit fixed point (signed)
Start ID = 180h
IMU ID = 1
CAN message #1:
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CAN ID = 181h
1st 16 bits: Channel 1 data
2nd 16 bits: Channel 2 data
3rd 16 bits: Channel 3 data
4th 16 bits: Channel 4 data |
CAN message #2:
| Code Block |
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CAN ID = 281h
1st 16 bits: Channel 5 data
2nd 16 bits: Channel 6 data
3rd 16 bits: Channel 7 data
4th 16 bits: Channel 8 data |
CAN message #3
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CAN ID = 381h
1st 16 bits: Channel 9 data
2nd 16 bits: Channel 10 data
3rd 16 bits: Channel 11 data
4th 16 bits: Channel 12 data |
CAN message #4:
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CAN ID = 481h
1st 16 bits: Channel 13 data
2nd 16 bits: Channel 14 data
3rd 16 bits: Channel 15 data
4th 16 bits: Channel 16 data |
Channel mode = CANopen
Value mode = 32-bit floating point
Start ID = 180h
IMU ID = 1
CAN message #1:
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CAN message #2:
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CAN message |
#4:
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CAN message #4:
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Channel mode = CANopen Value mode = 32-bit floating point Start ID = 180h IMU ID = 1 | CAN message |
#1:
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CAN message |
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CAN message |
#3:
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CAN message |
#4:
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Transmitted units in 32-bit float mode:
Data type | Unit |
Raw (uncalibrated) angular speed (gyroscope) | radians / s |
Raw (uncalibrated) acceleration (accelerometer) | g |
Raw (uncalibrated) magnetic field strength (magnetometer) | uT |
Euler angle | radians |
Linear acceleration | g |
Quaternion | normalized units |
In 16-bit integer modes values are multiplied with a constant factor after transmission to increase precision:
Data type | Unit | Factor |
Raw (uncalibrated) angular speed (gyroscope) | radians / s | 1000 |
Raw (uncalibrated) acceleration (accelerometer) | g | 1000 |
Raw (uncalibrated) magnetic field strength (magnetometer) | uT | 100 |
Angular Velocity | radians / s | 1000 |
Quaternion | normalized units | 10000 |
Euler angle | radians | 10000 |
Linear acceleration | g | 1000 |
Barometric pressure | kPa | 100 |
Altitude | m | 10 |
Temperature | °C | 100 |
Heave motion (optional) | m | 1000 |