Remote Compass Module
| Refer to COMPONENT INDEX . |
The compass feature provides the customer with current information about vehicle heading. The compass is visualized when the ignition is in either RUN or ACC states. The BCM determines whether or not a standalone compass module exists on the vehicle.
Compass Heading Calculations - If a standalone compass module is present and the radio is equipped with gyro, the BCM will ignore the data coming from the compass module and only use the data from the gyro for heading direction. The BCM is responsible for sending the heading direction to the IPC.
The compass gathers the true north position using the earths magnetic field and applies the compass variance to determine the compass direction. The compass master provides hysteresis to prevent the display heading from switching back and forth repeatedly while driving along a switch point. As part of the hysteresis, the compass master will not change the heading until the heading angle exceeds or drops below the normal switch point by 2.5 degrees or more. An example of this is that the switch point between north and north east is 22.5 degrees/ When driving north along that line, the compass master will hold the heading "N" until the heading angle reaches 25 degrees, then it may update to "NE". Consequently, it will not change back to "N' until the heading angle drops below 20 degrees.
Compass data transfer - The BCM communicates with the compass over the LIN bus. The compass sends heading direction, variance value, calibration mode status, calibration request and the state of calibration faults to the BCM.
The BCM sends to the compass the status of the vehicle (whether it is moving or not), the mounting orientation, the mounting angle and the request for calibration or changing in the variance. The BCM then broadcasts and sends the compass direction to the IPC.
Compass Variance Setting - The compass can only increment its variance zone value one step at a time. This requires that the BCM sends several increment requests to the compass if the compass variance is more than one variance away. The compass default value for the variance is set to the North East United State setting, or zone-8.
The compass is able to have its calibration and variance value saved in non volatile memory, eliminating the need of compass recalibration or reset of the variance every time the power cycles or a battery disconnect occurs.
Manual Compass Calibration - The customer is able to calibrate the compass manually when the system is supported by the compass module. When the customer selects to calibrate the compass, the BCM sends a LIN command to the compass module to calibrate. The compass module will then return a LIN signal to the BCM indicating that calibration is complete. Once this signal is received by the BCM, the BCM sends a CAN-IHS message to the IPC with the new compass data calibration information.