AN4504 datasheet(11/41 Pages) STMICROELECTRONICS

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AN4504

Reading angular rate data

The check performed at step 3 allows understanding whether the reading rate is adequate

compared to the data production rate. In case one or more angular rate samples have been

overwritten by new data, because of an insufficient reading rate, the ZYXOR bit of

STATUS_REG is set to 1.

The overrun bits are automatically cleared when all the data present inside the device have

been read and new data have not been produced in the meantime.

3.3

Using the data-ready (DRDY) signal

The device may be configured to have one HW signal to determine when a new set of

measurement data is available for reading. This signal is represented by the XYZDA bit of

STATUS_REG. The signal can be driven to the DRDY/INT2 pin by setting the I2_DRDY bit

of CTRL_REG3 to 1 and its polarity set to active-low or active-high through the H_Lactive bit

of CTRL_REG3 (see Section 5.1).

The data-ready signal rises to 1 when a new set of angular rate data has been generated

and it is available for reading.The interrupt is reset when the higher part of one of the

enabled channels has been read (29h, 2Bh, 2Dh).

Figure 1. Data ready signal

3.4

Using the block data update (BDU) feature

If reading the angular rate data is particularly slow and cannot be synchronized (or it is not

required) with either the XYZDA bit present inside the STATUS_REG or with the DRDY

signal, it is strongly recommended to set the BDU (block data update) bit in CTRL_REG4

to 1.

This feature avoids reading values (most significant and least significant parts of the angular

rate data) related to different samples. In particular, when the BDU is activated, the data

registers related to each channel always contain the most recent angular rate data produced

by the device, but, in case the reading of a given pair (i.e. OUT_X_H and OUT_X_L,

OUT_Y_H and OUT_Y_L, OUT_Z_H and OUT_Z_L) is initiated, the refresh for that pair is

blocked until both MSB and LSB parts of the data are read.

Note:

BDU only guarantees that OUT_X(Y, Z)_L and OUT_X(Y,Z)_H have been sampled at the

same moment. For example, if the reading speed is too slow, it may read X and Y sampled

at T1 and Z sampled at T2.

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