FXLS93421 datasheet(144/254 Pages) NXP

144 / 254 page

NXP Semiconductors

FXLS9xxxx

Dual channel inertial sensor

11.9 Arming function

When SPI mode is enabled via the COMMTYPE register, the device provides the option

for an arming function with 3 modes of operation. The operation of the arming function is

selected by the state of the ARM_CFG bits in the CHx_CFG_U4 registers.

See Section 14.5 for the operation of the Arming function with exception conditions. Error

conditions do not impact prior arming function responses. If an error occurs after an

arming activation, the corresponding pulse stretch for the existing arming condition will

continue. However, new sensor reads will not update the arming function regardless of

the sensor value.

11.9.1 Arming function: moving average mode

In moving average mode, the arming function runs a moving average on the offset

canceled output of the associated sensor channel DATATYPE0. The number of samples

used for the moving average (k) is programmable via the ARM_WS[1:0] bits in the

CHx_ARM_CFG registers. See Section 11.2.28.3 for register details.

(16)

Where n is the current sample.

The sample rate for each channel is determined by the rate of the SPI sensor data

requests. At the falling edge of SS_B for a sensor data SPI response for SOURCEID_0

(channel 0) or SOURCEID_2 (channel 1), the moving average for the associated channel

is updated with a new sample. See Figure 56. The arming function input data rate can

be down sampled as described in Section 11.9.4. The SPI sensor data sample rate must

meet the minimum time between requests (tACC_REQ_x) specified in Section 10.13.

The moving average output is compared against positive and negative thresholds that

are individually programmed for each channel via the CHx_ARMT_x registers. See

Section 11.2.29 for register details. If the moving average equals or exceeds either

threshold, an arming condition is indicated, the arming pin output is asserted for the

associated channel, and the pulse stretch counter is set as described in Section 11.9.5.

The arming pin output is deasserted only when the pulse stretch counter expires.

Figure 56 shows the arming output operation for different SPI conditions.

aaa-030639

POSITIVE

MOVING AVERAGE

PULSE STRETCH

GATING

ARM

ARM_WS_P[1:0]

OC_out[12:3]

ARM_T_P[7:0]

NEGATIVE

MOVING AVERAGE

ARM_WS_N[1:0]

ARM_T_N[7:0]

I/O

ARM_PS[3:0]

Figure 56. Arming function block diagram - moving average mode

FXLS9xxxx

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Product data sheet

Rev. 6 — 8 February 2021

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