Sensor

40

Freescale Semiconductor, Inc.

MMA65xx

3.8.10.4

Arming Pulse Stretch Function

A pulse stretch function can be applied to the arming outputs in moving average mode, or count mode.

If the pulse stretch function is not used (APS_X[1:0] = ‘00’ or APS_Y[1:0] = ‘00’), the arming output is asserted if and only if

an arming condition exists for the associated axis after the most recent evaluated sample. The arming output is de-asserted if

and only if an arming condition does not exist for the associated axis after the most recent evaluated sample.

If the pulse stretch function is used, (APS_X[1:0] not equal ‘00’ or APS_Y[1:0] not equal ‘00’), the arming output is controlled

only by the value of the pulse stretch timer value. If the pulse stretch timer value is non-zero, the arming output is asserted. If the

pulse stretch timer is zero, the arming output is de-asserted. The pulse stretch counter continuously decrements until it reaches

zero. The pulse stretch counter is reset to the programmed pulse stretch value if and only if an arming condition exists for the

associated axis after the most recent evaluated sample. Reference Figure 28.

The desired pulse stretch time is individually programmable for each axis via the APS_X[1:0] and APS_Y[1:0] bits in the ARM-

CFG register.

Exception conditions listed in Section 4.5 do not impact prior arming function responses. If an exception occurs after an arming

activation, the corresponding pulse stretch for the existing arming condition will continue. However, new acceleration reads will

not reset the pulse stretch counter regardless of the acceleration value.

3.8.10.5

Arming Pin Output Structure

The arming output pin structure can be set to active high, or active low with the A_CFG bits in the DEVCFG register as de-

scribed in Section 3.1.6.6. The active high and active low pin output structures are shown in Figure 31.

Figure 31. Arming Function - Pin Output Structure

Arm Function

ARM_x

Gating

Arm Function

ARM_x

Gating

Open Drain, Active High

Open Drain, Active Low