AN3393 datasheet(46/103 Pages) STMICROELECTRONICS

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State machine

AN3393

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DocID018750 Rev 4

DCC = DCC -1

When DCC is equal to 0, the current sample is used as new input for State Machine 2.

DCC = DES2 (initial decimation value)

5.4.2

DIFF calculation

This function is available only in State Machine 2. It is a data process method which

calculates:

diff2 - difference between current data (X, Y, Z) and previous data.

cs - difference between current data (X, Y, Z) and constant shift registers.

diff2:

–

Previous samples (X,Y,Z) selected for calculations

–

Diff2 = current measured - previous sample

After calculation, the new samples are moved to the previous samples and the “old”

previous samples are discarded.

cs:

Constant shift acts like temporary offset shift. Constant shift initial values (stored in registers

13h, 14h and 15h) are used to calculate DIFF results:

–

cs = current measured - constant shift

To enable DIFF calculation on State Machine 2, bits RADI and D_CS must be set in the

SETT2 register (7Bh).

Note:

DIFF calculation is not applied to the vector data (V). It is applied to (X, Y, Z) data only.

5.5

State machine description

A state machine is a set of defined states, with inputs, outputs and transitions between

states. In the LIS3DSH accelerometer, two state machines are available. They can run

either independently or synchronized, but always using the same input data.

For each new data sample, the State Machine 1 is performed first, then State Machine 2

with the same common internal input data.

Input data are not changed during state machine executions. Calculation results are stored

in temporary parameters.

A simple state machine is shown in Figure 8.

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