Sensors

Freescale Semiconductor

19

MMA690xQ

3.1.2

Exception Priority

Table 3-1 provides a summary of exception conditions and order of priority.

If an offset fault condition is detected simultaneously in both the X- and Y-axes, only the X-axis exception is reported by the

device. Hold condition and self-test exceptions have equal priority; if both exceptions exist simultaneously, both are reported by

the device.

3.2

COMMUNICATIONS PROTOCOL

The Communications Protocol provides 11-bit acceleration data along with enhanced status notification in the event that an

exception condition is detected. All transfers are 16-bits in length, with the intended operation indicated by a two-bit transfer type

code transmitted by the SPI master.

Device response depends upon the transfer type code and the internal state of the device. If no exception condition has been

detected, the device returns register or acceleration data as requested. If an exception condition exists, response depends upon

the requested operation and the exception. Exceptions are divided into four classes: behavioral, reset, transient, and critical. Cer-

tain operations, such as register data write and register pointer write, will not be completed if an exception condition is detected

during the associated SPI transfer. All exception conditions detected by MMA690xQ are listed in Table 3-1. Response to excep-

tions is described below, and summarized in Table 3-3.

If both T1 and T0 are set to a logic ‘1’ state, an invalid axis selection exception will be reported by the device.

3.2.1

Device Response

Device response depends upon exception conditions which may be present at the time the transfer takes place. In case of

multiple exceptions, the exception class of highest priority will determine response.

Table 3-1. Exception Conditions

Condition

Status Bit

Class

SPI Clock Fault, Previous Transfer

—

Transient

—

Transient

Internal Data Error

IDE

Critical Error

Internal Oscillator Fault

—

Critical Error

Device Initialization

DEVINIT

Reset

Device Reset

DEVRES

Reset

Temperature Fault

TF

Critical Error

Invalid Axis Selection

—

Transient

Hold Condition

—

Behavioral

Self-test

—

Behavioral

Table 3-2. Transfer Type Codes

T1

T0

Transfer Type

0

0

Register Operation

0

1

X-axis acceleration data

1

0

Y-axis acceleration data

1

1

Unused