Sensors

14

Freescale Semiconductor

MMA690xQ

2.6

INTERNAL RESET CONTROLLER

Four conditions can result in an internal reset. The initial power-on condition always results in a reset condition An internal

voltage monitor will assert reset when the supply voltage or a regulated output voltage falls below specified limits. This is referred

to as a low voltage reset. Externally, a hardware reset can be initiated by holding SCLK high and driving the CS pin low for 512

μs.

Finally, the device can be reset through a series of register write operations, as described in Section 2.1.3.1.

2.7

CONTROL LOGIC

A control logic block coordinates a number of activities within the device. These include:

• Post-reset device initialization

• Self-test

• Operating mode selection

• Data array programming

• Device support data transfers

2.8

TEMPERATURE SENSOR

A temperature sensor provides input to the digital signal processing block. Device temperature is incorporated into a correction

value, which is applied to each acceleration result. The upper eight bits of the temperature sensor value are accessible through

the TEMP register, described in Section 2.1.4. The temperature sensor output is continuously compared to under- or over-tem-

perature limits of approximately -40 and +110 °C, respectively. A temperature fault condition is indicated if the temperature sensor

value exceeds the under- or over-temperature limit.

2.8.1

TEMPERATURE SENSOR MONITOR

A monitor circuit associated with the temperature sensor is provided. The monitor will detect over- or under-temperature con-

ditions as well as rapid fluctuations in temperature sensor output such as would be related to failure of the sensor. If a temperature

related fault is detected, an error condition is indicated in lieu of acceleration data.

Rapid fluctuation of the temperature sensor output is detected by comparing the value of each sample to the previous value.

This operation, as well as temperature limit detection is illustrated in Figure 2-5. A fault condition is indicated if predetermined

limits are exceeded.