In addition to the streaming Serial protocol over USB, navX-Micro may be accessed over the I2C bus, using a register-based protocol.
Register-based protocol overview
Unlike the streaming Serial protocol, which periodically sends out updates messages whenever new data is available, the register based protocol is a “polled” interface, in that the consumer of the navX-Micro data (in this case referred to as a “bus master”) can request data from the navX-Micro at any time. At the same time, when using the register-based protocol the bus master does not know when new data is available.
To help this situation, a timestamp – which is updated whenever new data is available – is made available. Therefore, the general approach to ensure each new data sample is retrieved is to regularly (at the navX-Micro update rate) retrieve both the timestamp and the data of interest), and if the timestamp differs from the previous timestamp by the update rate as expressed in milliseconds, then the data sample just retrieved is current, and no data has been missed.
I2C Overview
The navX-Micro responds to 7-bit address 50 (0x32) on the I2C bus. If accessing the navX-Micro via the I2C bus, ensure that no other device at that address is on the same bus.
The navX-Micro I2C bus operates at a speed up to 400Khz.
When accessing the navX-Micro via the I2C bus, this following pattern is used:
– The I2C bus master sends the navX-Micro I2C address. The highest bit is set to indicate the bus master intends to write to the navX-MXP. If the highest bit is clear, this indicates the bus master intends to read from the navX-MXP.
– The I2C bus master next sends the starting register address it intends to write to or read from.
– The I2C bus master next initiates I2C an bus transaction. The navX-MXP supports I2C burst mode for read operations, therefore the navX-MXP will respond with register values as long as the I2C bus master continues the transaction, and as long as the last register address has not yet been reached.
If instead the I2C bus master intends to write data to a writable navX-MXP register, the bus master should transmit the new register value immediately after sending the register address.
navX-Micro Register Data Types
All multi-byte registers are in little-endian format.
All registers with ‘signed’ data are 2’s-complement.
| Data Type | Range | Byte Count |
| Unsigned Byte | 0 to 255 | 1 |
| Unsigned Short | 0 to 65535 | 2 |
| Signed Short | -32768 to 32768 | 2 |
| signed hundredths | -327.68 to 327.67 | 2 |
| Unsigned Hundredths | 0.0 to 655.35 | 2 |
| Signed Thousandths | -32.768 to 32.767 | 2 |
| Signed Pi Radians | -2 to 2 | 2 |
| Q16.16 | -32768.9999 to 32767.9999 | 4 |
| Unsigned Long | 0 to 4294967295 | 4 |
*Unsigned Hundredths: original value * 100 to rounded to nearest integer
*Signed Hundredths: original value * 100 rounded to nearest integer
*Signed Thousandths: original value * 1000 rounted to nearest integer
*Signed Pi Radians: original value * 16384 rounded to nearest integer
navX-Micro Register Map
| Address (Hex) | Name | Access | Range/Data Type |
| 0x00 | WhoAmI | Read-only | 50 (0x32): navX-MXP |
| 0x01 | Board Revision | Read-only | Unsigned byte |
| 0x02 | Firmware Major Version | Read-only | Unsigned byte |
| 0x03 | Firmware Minor Version | Read-only | Unsigned byte |
| 0x04 | Update Rate | Read/write | Unsigned byte (Hz) |
| 0x05 | Accel FSR | Read-only | Unsigned byte (Degrees/Sec) |
| 0x06-0x07 | Gyro FSR | Read-only | Unsigned short(G) |
| 0x08 | Operational Status | Read-only | See NAVX_OP_STATUS |
| 0x09 | Calibration Status | Read-only | See NAVX_CAL_STATUS |
| 0x0A | Self-test Status | Read-only | See NAVX_SELFTEST_STATUS |
| 0x0B | Capability Flags (low) | Read-only | See NAVX_CAPABILITY |
| 0x0C | Capability Flags (high) | Read-only | “” |
| 0x0D-0x0F | n/a | Read-only | |
| 0x10 | Sensor Status (low) | Read-only | See NAVX_SENSOR_STATUS |
| 0x11 | Sensor Status (high) | Read-only | “” |
| 0x12-0x15 | Current Timestamp | Read-only | Unsigned long |
| 0x16-0x17 | Yaw | Read-only | Signed Packed Hundredths (Degrees) |
| 0x18-0x19 | Pitch | Read-only | Signed Packed Hundredths (Degrees) |
| 0x1A-0x1B | Roll | Read-only | Signed Packed Hundredths (Degrees) |
| 0x1C-0x1D | Heading | Read-only | Unsigned Packed Hundredths (Degrees) |
| 0x1E-0x1F | Fused Heading | Read-only | Unsigned Packed Hundredths (Degrees)) |
| 0x20-0x23 | Altitude | Read-only | Q16.16 – NavX-MXP Aero Only (Meters) |
| 0x24-0x25 | Linear Acceleration (X) | Read-only | Signed Thousandths (G) |
| 0x26-0x27 | Linear Acceleration (Y) | Read-only | Signed Thousandths (G) |
| 0x28-0x29 | Linear Acceleration (Z) | Read-only | Signed Thousandths (G) |
| 0x2A-0x2B | Quaternion (W) | Read-only | Signed Pi Radians (Pi Radians) |
| 0x2C-0x2D | Quaternion (X) | Read-only | Signed Pi Radians (Pi Radians) |
| 0x2E-0x2F | Quaternion (Y) | Read-only | Signed Pi Radians (Pi Radians) |
| 0x30-0x31 | Quaternion (Z) | Read-only | Signed Pi Radians (Pi Radians) |
| 0x32-0x33 | MPU Temperature | Read-only | Signed Packed Hundredths (C) |
| 0x34-0x35 | Calibrated Gyro (X) | Read-only | Signed Short (Degrees/sec in device units) |
| 0x36-0x37 | Calibrated Gyro (Y) | Read-only | Signed Short (Degrees/sec in device units) |
| 0x38-0x39 | Calibrated Gyro (Z) | Read-only | Signed Short (Degrees/sec in device units) |
| 0x3A-0x3B | Calibrated Acceleration (X) | Read-only | Signed Short (G in device units) |
| 0x3C-0x3D | Calibrated Acceleration (Y) | Read-only | Signed Short (G in device units) |
| 0x3E-0x3F | Calibrated Acceleration (Z) | Read-only | Signed Short (G in device units) |
| 0x40-0x41 | Calibrated Magnetometer (X) | Read-only | Signed Short (uTesla in device units) |
| 0x42-0x43 | Calibrated Magnetometer (Y) | Read-only | Signed Short (uTesla in device units) |
| 0x44-0x45 | Calibrated Magnetometer (Z) | Read-only | Signed Short (uTesla in device units) |
| 0x46-0x49 | Barometric Pressure | Read-only | Q16.16 (millibars) |
| 0x4A-0x4B | Pressure Sensor Temperature | Read-only | Signed Packed Hundredths (C) |
| 0x4C-0x4D | Calibrated Yaw Offset | Read-only | Signed Hundredths (Degrees) |
| 0x4E-0x4F | Calibrated Quaternion Offset (W) | Read-only | Signed Short Ratio (Ratio) |
| 0x50-0x51 | Calibrated Quaternion Offset (X) | Read-only | Signed Short Ratio (Ratio) |
| 0x52-0x53 | Calibrated Quaternion Offset (Y) | Read-only | Signed Short Ratio (Ratio) |
| 0x54-0x55 | Calibrated Quaternion Offset (Z) | Read-only | Signed Short Ratio (Ratio) |
| 0x56 | Integration Control | Read/write | See NAVX_INTEGRATION_CTL (v1.2 firmware and higher) |
| 0x58-0x5B | Integrated Velocity (X) | Read-only | Q16.16 (Meters/sec) (v1.2 firmware and higher) |
| 0x5C-0x5F | Integrated Velocity (Y) | Read-only | Q16.16 (Meters/sec) (v1.2 firmware and higher) |
| 0x60-0x63 | Integrated Velocity (Z) | Read-only | Q16,16 (Meters/sec) (v1.2 firmware and higher) |
| 0x64-0x67 | Integrated Displacement (X) | Read-only | Q16.16 (Meters) (v1.2 firmware and higher) |
| 0x68-0x6B | Integrated Displacement (Y) | Read-only | Q16,16 (Meters) (v1.2 firmware and higher) |
| 0x6C-0x6F | Integrated Displacement (Z) | Read-only | Q16.16 (Meters) (v1.2 firmware and higher) |
NAVX_OP_STATUS
| Meaning | Value |
| NAVX_OP_STATUS_INITIALIZING | 0x00 |
| NAVX_OP_STATUS_SELFTEST_IN_PROGRESS | 0x01 |
| NAVX_OP_STATUS_ERROR | 0x02 |
| NAVX_OP_STATUS_IMU_AUTOCAL_IN_PROGRESS | 0x03 |
| NAVX_OP_STATUS_NORMAL | 0x04 |
NAVX_SENSOR_STATUS
| Meaning | Value |
| NAVX_SENSOR_STATUS_MOVING | 0x01 |
| NAVX_SENSOR_STATUS_YAW_STABLE | 0x02 |
| NAVX_SENSOR_STATUS_MAG_DISTURBANCE | 0x04 |
| NAVX_SENSOR_STATUS_ALTITUDE_VALID | 0x08 |
| NAVX_SENSOR_STATUS_SEALEVEL_PRESS_SET | 0x10 |
| NAVX_SENSOR_STATUS_FUSED_HEADING_VALID | 0x20 |
NAVX_CAL_STATUS
| Meaning | Value |
| NAVX_CAL_STATUS_IMU_CAL_INPROGRESS | 0x00 |
| NAVX_CAL_STATUS_IMU_CAL_ACCUMULATE | 0x01 |
| NAVX_CAL_STATUS_IMU_CAL_COMPLETE | 0x02 |
| NAVX_CAL_STATUS_MAG_CAL_COMPLETE | 0x04 |
| NAVX_CAL_STATUS_BARO_CAL_COMPLETE | 0x08 |
NAVX_SELFTEST_STATUS
| Meaning | Value |
| NAVX_SELFTEST_STATUS_COMPLETE | 0x80 |
| NAVX_SELFTEST_RESULT_GYRO_PASSED | 0x01 |
| NAVX_SELFTEST_RESULT_ACCEL_PASSED | 0x02 |
| NAVX_SELFTEST_RESULT_MAG_PASSED | 0x04 |
| NAVX_SELFTEST_RESULT_BARO_PASSED | 0x08 |
NAVX_CAPABILITY
| Meaning | Value |
| NAVX_CAPABILITY_FLAG_OMNIMOUNT | 0x04 |
| NAVX_CAPABILITY_FLAG_OMNIMOUNT_CONFIG_MASK | 0x38 |
| NAVX_CAPABILITY_FLAG_VEL_AND_DISP | 0x40 |
| NAVX_CAPABILITY_FLAG_VEL_AND_DISP | 0x80 |
NAVX_OMNIMOUNT_CONFIG
| Meaning | Value |
| OMNIMOUNT_DEFAULT (Z Axis, Up) | 0x00 |
| OMNIMOUNT_YAW_X_UP | 0x01 |
| OMNIMOUNT_YAW_X_DOWN | 0x02 |
| OMNIMOUNT_YAW_Y_UP | 0x03 |
| OMNIMOUNT_YAW_Y_DOWN | 0x04 |
| OMNIMOUNT_YAW_Z_UP | 0x05 |
| OMNIMOUNT_YAW_Z_DOWN | 0x06 |
NAVX_INTEGRATION_CTL
| Meaning | Value |
| NAVX_INTEGRATION_CTL_RESET_VEL_X | 0x01 |
| NAVX_INTEGRATION_CTL_RESET_VEL_Y | 0x02 |
| NAVX_INTEGRATION_CTL_RESET_VEL_X | 0x04 |
| NAVX_INTEGRATION_CTL_RESET_DISP_X | 0x08 |
| NAVX_INTEGRATION_CTL_RESET_DISP_Y | 0x10 |
| NAVX_INTEGRATION_CTL_RESET_DISP_X | 0x20 |
| NAVX_INTEGRATION_CTL_RESET_YAW | 0x80 |