ADIS16480SLASHPCBZ datasheet(28/40 Pages) AD

28 / 40 page

ADIS16480

Data Sheet

Rev. 0 | Page 28 of 40

REFERENCE FRAME

During the power-on initialization and reset recovery opera-

tions, the ADIS16480 sets the accelerometer and magnetometer

references for use in the orientation computation. During this

process, the gravity vector becomes the accelerometer reference

and the magnetometer reference computation includes the

following steps: measure horizontal and vertical components

of the magnetic field and align the horizontal component to

magnetic north. This also measures the inclination, which

removes this requirement from an external system. The resulting

reference frame is a local ENU inertial frame formed by the

y-axis pointing at magnetic north, the z-axis pointing up, and

the x-axis completing the right-hand frame by pointing east.

REFERENCE TRANSFORMATION MATRIX

The reference transformation matrix, RIJ, provides a user-

programmable alignment function for orientation alignment

to a local navigation frame. Another common name for this

function in navigation system literature is the coordinate

transformation matrix.













When this matrix is equal to an identify matrix (factory

default), the local navigation frame matches true level, with

respect to gravity, and magnetic north. The tare command

automatically calculates and loads the matrix values that

establish the current ADIS16480 orientation as the reference

orientation. When the ADIS16480 is in the desired reference

orientation, initiate the tare command by setting GLOB_CMD[8]

= 1 (DIN = 0x8003, then DIN = 0x8301, see Table 146).

Each element in this matrix is associated with a register that

provides read and write access. See Table 84 through Table 92,

for these registers. Use these registers to define the local

navigation frame, based on system generated requirements.

Each element is the cross product of the unit vectors that

describe the axes of the two frames, which are equal to the

cosines of the angles between the axes. Units of rotation vary

by ±1. When writing to these registers, write to R33 last because

a write to the upper byte of this register causes all nine registers

to update inside of the ADIS16480.

Table 84. REFMTX_R11 (Page 2, Base Address = 0x62)

Bits

Description (Default = 0x7FFF)

Sign bit

[14:0]