AN4506 datasheet(13/47 Pages) STMICROELECTRONICS

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AN4506

Reading angular rate data

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Figure 2. Data-ready signal

3.4

Using the block data update (BDU) feature

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

not required) with either the XYZDA bit in the STATUS register or with the DRDY signal, it is

strongly recommended to set the BDU (block data update) bit to 1 in the CTRL4 register.

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, if 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.

Data must be read starting from the lower address.

3.5

DEN function

The L3GD20H allows external trigger level recognition through enabling the EXTRen (bit7)

and LVLen (bit6) bits in CTRL2 (21h) and the IMPen (bit3) bit of CTRL4. Three different

modes can be used: level-sensitive, pulse-sensitive and edge-sensitive trigger.

3.5.1

Level-sensitive trigger stamping (LVLen = 1; EXTRen = 0; IMPen = 0)

Once enabled, the DEN logical value replaces the less significant bit of X, Y and Z data for

the axis selected through the Xen, Yen, and Zen bits in CTRL_REG1 (20h).

Data are stored inside the FIFO with the internally selected ODR.

Table 6. DEN configurations

EXTRen

LVLen

IMPen

Function

Level sensitive

Pulse sensitive

Edge sensitive

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