AN4650 datasheet(29/102 Pages) STMICROELECTRONICS

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AN4650

Reading output data

102

3.3

Using the data-ready signal

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

measurement data is available for reading.

For the accelerometer sensor, the data-ready signal is represented by the XLDA bit of the

STATUS_REG register. The signal can be driven to the INT1 pin by setting to 1 the

INT1_DRDY_XL bit of the INT1_CTRL register and to the INT2 pin by setting to 1 the

INT2_DRDY_XL bit of the INT2_CTRL register.

For the gyroscope sensor, the data-ready signal is represented by the GDA bit of the

STATUS_REG register. The signal can be driven to the INT1 pin by setting to 1 the

INT1_DRDY_G bit of the INT1_CTRL register and to the INT2 pin by setting to 1 the

INT2_DRDY_G bit of the INT2_CTRL register.

The data-ready signal rises to 1 when a new set of 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 for the accelerometer; 23h, 25h, 27h for the

gyroscope).

Setting the DRDY_MASK bit of the CTRL4_C register to 1, the accelerometer and

gyroscope data-ready signals are masked until the settling of the sensor filters is completed.

Figure 6. Data-ready signal

3.4

Using the block data update (BDU) feature

If reading the accelerometer/gyroscope data is particularly slow and cannot be synchronized

(or it is not required) with either the XLDA/GDA bits in the STATUS_REG register or with the

DRDY signal driven to the INT1/INT2 pins, it is strongly recommended to set the BDU (block

data update) bit to 1 in the CTRL3_C register.

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

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

registers related to each channel always contain the most recent output data produced by

the device, but, in case the read of a given pair (i.e. OUTX_H_XL(G) and OUTX_L_XL(G),

OUTY_H_XL(G) and OUTY_L_XL(G), OUTZ_H_XL(G) and OUTZ_L_XL(G)) 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 the LSB part and MSB part have been sampled at the same

moment. For example, if the reading speed is too slow, X and Y can be read at T1 and Z

sampled at T2.

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