MMA685X datasheet(38/52 Pages) FREESCALE

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Sensors

Freescale Semiconductor, Inc.

MMA685x

3.8.9.3

Arming Function: Unfiltered Mode

On the falling edge of CS for an acceleration response, the most recent available DSP sample is compared against positive

and negative thresholds that are programmed via the ARMT_x registers. Reference Section 3.1.9 for register details. If the sam-

ple equals or exceeds either threshold, an arming condition is indicated.

Once an arming condition is indicated for the ARM output is asserted when CS is asserted and the MISO data includes an

acceleration response.

The pulse stretch function is not applied in Unfiltered mode.

Figure 27 contains a block diagram of the Arming Function operation in Unfiltered Mode. Figure 28 shows the Arming output

operation under the different SPI request conditions.

Figure 27. Arming Function Block Diagram - Unfiltered Mode

Figure 28. MMA685x Arming Conditions, Unfiltered Mode

ACFG[2]

AXIS Select

ARM

I/O

ACFG[1]

ARMING FUNCTION

Interpolated Sample Rate

X-Axis Arm Condition

Not Present

X-Axis Data Latched for

Arm Function and SPI

SCLK

MOSI

MISO

Request X-Axis

X-Axis Response

Request X-Axis

X-Axis Response

ARM

X-Axis Response

X-Axis Arm Condition

Not Present

X-Axis Arm Condition

Not Present

X-Axis Arm Condition

Present

tARM_UF_DL

tARM_UF_ASSERT

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