AHRS400 Series User’s Manual
Page 8 Doc# 7430-0004-01 Rev. A
the web at http://www.xbow.com. The source code has a .vi file format and
requires a National Instruments LabView 5.0 or newer license to use.
The DMU baud rate can be changed per the following procedure:
1. Start with the DMU connected to the serial interface, with
your software set to the default baud rate of 38,400.
2. Send the ASCII character “b” (0x62 hex) to the DMU. In a
terminal program like Windows HyperTerminal or ProComm,
this means simply type the letter “b”. The DMU is case
sensitive. The DMU will respond “B” (0x42 hex).
3. Now change the baud rate of your terminal software.
4. Send the ASCII character “a” (61 hex). The DMU will detect
the character and automatically match the baud rate your
software is using. Upon successful operation, the DMU will
return the character “A” (0x41 hex) at the new baud rate.
5. You can now use the DMU at the new baud rate.
The new baud rate setting is not permanent; therefore, this process must be
repeated after any power reset.
3.4 Measurement Modes
The AHRS400 Series is designed to operate as a complete attitude and
heading reference system. You can also use the DMU as a nine-axis sensor
module. The AHRS can be set to operate in one of three modes: voltage
mode, scaled sensor mode, or angle (VG) mode. The measurement mode
selects the information that is sent in the data packet over the RS-232
interface. See the “Data Packet Format” section for the actual structure of
the data packet in each mode.
3.4.1 Voltage Mode
In voltage mode, the analog sensors are sampled and converted to digital
data with 1 mV resolution. The digital data represents the direct voltage
output of the sensors. The data is 12-bit, unsigned. The value for each
sensor is sent as 2 bytes in the data packet over the serial interface. A single
data packet can be requested using a serial poll command or the DMU can
be set to continuously output data packets to the host.
The voltage data is scaled as:
voltage = data*(5 V)/2
12
where voltage is the voltage measured at the sensor, and data is the value
of the unsigned 16-bit integer in the data packet. Note that although the
data is sent as 16-bit integers, the data has a resolution of only 12 bits.
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