AN3393 datasheet(73/103 Pages) STMICROELECTRONICS

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AN3393

Axis mask filter

103

case of two axes triggering the state machine at the same time, the temporary output mask

selects only the first axis by following the order: X, Y, Z and V. Once the axis has been

selected it remains the only one considered until the state machine program restarts (after

the END state or a RESET condition). An example of how the temporary mask is updated

and how its value affects the state machine is shown in Figure 14.

Figure 14. Temporary mask example

The example of Figure 14 starts with the following settings:

–

MASK1 = F0h (+-x enabled, +-y enabled);

–

ABS = 0 in SETT1 register (unsigned threshold);

–

TMASK1 = 0 (temporary mask default value).

Moreover, the R_TAM bit in the SETT1 register is set to 0, so that the mask is frozen on the

axis that triggers the condition.

In the first phase (State 1), the NEXT condition (GNTH1 in this case) is evaluated on all the

axes specified by MASK1 (in this case: +-x and +-y). At the beginning, both X and Y are

lower than threshold 1, but after a while, acceleration on the Y-axis exceeds threshold 1. So,

the value +y is stored in the temporary mask, and the state machine is triggered on this axis

in the following conditions.

In the second phase (State 2), a “lower than threshold 1” condition is evaluated. This

condition is evaluated just on the positive Y-axis regardless of whether the acceleration on

the X-axis is lower than threshold 1. This is because TMASK = +y and the R_TAM bit was

set to 0 in the SETT1 register.

Note that if the R_TAM bit was set to 1 (instead of 0), then the condition LNTH1 would be

valid on the first sample evaluated in the second phase (State 2). In fact, when the R_TAM

bit is 1, the standard mask (MASK1) is always evaluated regardless of the value in the

temporary mask.

AM14780V1

AN3393 датащи(PDF) 73 Page - STMicroelectronics