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Modifications reserved | Data subject to change without notice

Document number: BST-BMA456-DS000-08

Revision_3.5_032025

Sensor Time

The BMA456 supports the concept of sensortime. Its core element is a free running counter with a

width of 24 bits. It increments with a resolution of 39.0625us. The user can access the current state of

the counter by reading registers SENSORTIME_0 to SENSORTIME_2.

All sensor events e.g. updates of data registers are synchronous to this sensor time register as

defined in the table below. With every update of the data register or the FIFO, a bit m in the registers

SENSORTIME_0 to SENSORTIME_2 toggles where m depends on the output data rate for the data

shows which bit toggles for which update rate of data register and FIFO

Bit m in sensor_time

17 16

Resolution [s]

327.68 163.84 81.92 40.96 20.48 10.24 5.12 2.56

Update rate [Hz]

0.0031 0.0061 0.012 0.024 0.049 0.10 0.20 0.39

The sensortime is synchronized with the data capturing in the data register and the FIFO. Between the

data sampling and the data capturing there is a delay which depends on the settings in the Register

ACC_CONF. The sensortime supports multiple seconds of sample counting and a sub-microsecond

resolution, see Register SENSORTIME_0 for details.

Burst reads on the registers SENSORTIME_0 to SENSORTIME_2 deliver always consistent values,

i.e. the value of the register does not change during the burst read.

Configuration Changes

If accelerometer configuration settings in registers ACC_CONF, ACC_RANGE, or AUX_CONF are

changed while the accelerometer (PWR_CTRL.acc_en = 0b1) or auxiliary sensor

(PWR_CTRL.aux_en = 0b1) is enabled, the configuration changes are not immediately applied. The

configuration changes become effective if a sampling event for the currently active ODR coincides with

a sampling event for the newly requested ODR on the sensortime sampling grid. In the case where the

currently active ODR equals the newly requested ODR, the configuration changes become effective at

the next sampling event. See also following figure.

Bit m in sensor_time 15

12 11 10 9

Resolution [ms]

1280 640 320 160 80 40 20 10 5 2.5 1.250 0.625 0.3125 0.156 0.078 0.039

Update rate [Hz]

0.78 1.56 3.125 6.25 12.5 25 50 100 200 400 800 1600 3200

BMA456 Datasheet(PDF) 21 Page - Bosch Sensortec GmbH