Sensors

40

Freescale Semiconductor, Inc.

MMA685x

3.9

Serial Peripheral Interface

MMA685x includes a Serial Peripheral Interface (SPI) to provide access to the configuration registers and digital data. Refer-

ence Section 4 for details regarding the SPI protocol and available commands.

3.10

Device Initialization

Following power-up, under-voltage reset, or a SPI reset command sequence, MMA685x proceeds through an internal initial-

ization process as shown in Figure 31. Figure 31 also shows the MMA685x performance for an example external system level

initialization procedure.

Figure 31. Initialization Process

Dly

POR

OTP Copy to

Mirror Registers

Offset Cancellation

Startup Phase 2

Initialize R/W

Registers to

Desired State

Verify

Offset

Verify

Self Test &

ARM Asserted

Offset Cancellation

Startup Phase 1

Offset Cancellation

Startup Phase 3

Offset Cancellation

Normal Mode

Ready for SPI

Command

ENDINIT Clear

Dly

Re-Initialize

R/W Registers

(if needed)

Activate

Self Test

Internal

Offset Error

Corrected to ‘0’

DeActivate

Self Test

Normal

Mode

Internal Initialization

External Initialization

Delay

DeAssertion

Dependent on Pulse

Stretch and/or Arming Mode

Assertion

Dependent on

Arming Mode

Set ENDINIT

Read DEVSTAT

to clear flags

Re-read DEVSTAT

to verify Status

and

ST

ARM

Notes:1) Self Test can be enabled and evaluated simultaneously to reduce test time.

For failure mode coverage of the arming pins and of potential common axis failures, Freescale recommends independent self test activation.

Verify

Offset &

ARM DeAsserted

Dly