Sensors

Freescale Semiconductor, Inc.

49

MMA685x

4.5.7

ΣΔ Over Range

If a

ΣΔ Over Range failure is present as described in Section 3.11.2, MMA685x will respond to acceleration data requests with

a “Valid Acceleration Data Request” response, but the Status bits (S[1:0]) will be set to ‘10’. The arming function will be updated

on Acceleration Data Request commands even if a

ΣΔ Over Range is detected. Once the over range condition is removed,

MMA685x will respond to acceleration requests with a “Valid Acceleration Data Request” response with the Status bits (S[1:0])

set to ‘10’ on the next SPI transfer, and a “Valid Acceleration Data Request” response with normal status on subsequent SPI

transfers. The SDOV bit in the DEVSTAT register will remain set until a read of the DEVSTAT register occurs.

The PCM output is not affected by the

ΣΔ over range condition.

Register operations will be executed as specified in Section 4.4.

4.6

Initialization SPI Response

The first data transmitted by MMA685x following reset is the SPI Error response shown in Table 27. This ensures that an un-

expected reset will always be detectable. MMA685x will respond to all acceleration data requests with the “Invalid Acceleration

Data Request” response until the DEVRES bit in the DEVSTAT register is cleared via a read of the DEVSTAT register. The arming

function will not be updated on Acceleration Data Request commands until the DEVRES bit in the DEVSTAT register is cleared.

4.7

Acceleration Data Representation

Acceleration values are determined from the 10-bit digital output (DV) using the following equations:

The linear range of digital values for signed data is -480 to +480, and for unsigned data is 32 to 992. Resulting ranges and

some nominal acceleration values are shown in Table 31.

vant parameters are specified in Section 2.4.

Acceleration

Sensitivity

LSB

DV

512

–

()

×

=

Acceleration

Sensitivity

LSB

DV

×

=

For Signed Data

For Unsigned Data

Table 31. Nominal Acceleration Data Values

Unsigned

Digital Value

Signed

Digital Value

Nominal Acceleration

Trimmed for

Maximum Sensitivity

(g)

Trimmed for

Maximum Range

(g)

993 - 1023

481 - 511

Unused

992

480

19.666

117.19

991

479

19.625

116.94

•

•

•

•

•

•

•

•

•

•

•

•

514

2

+0.082

+0.488

513

1

+0.041

+0.244

512

0

0

0

511

-1

-0.041

-0.244

510

-2

-0.082

-0.488

•

•

•

•

•

•

•

•

•

•

•

•

33

-479

-19.625

-116.94

32

-480

-19.666

-117.19

1 - 31

-481 to -511

Unused

0

-512

Fault