Sensor

20

Freescale Semiconductor, Inc.

MMA65xx

The values programmed into the threshold registers are the threshold values used for the arming function as described in

Section 3.8.10. The threshold registers hold independent unsigned 8-bit values for each axis and polarity. Each threshold incre-

ment is equivalent to one output LSB. Table 21 shows examples of some threshold register values and the corresponding thresh-

old.

If either the positive or negative threshold for one axis is programmed to $00, comparisons are disabled for only that polarity.

The arming function still operates for the opposite polarity. If both the positive and negative arming thresholds for one axis are

programmed to $00, the Arming function for the associated axis is disabled, and the associated output pin is disabled, regardless

of the value of the A_CFG bits in the DEVCFG register.

3.1.11

Device Status Register (DEVSTAT)

The device status register is a read-only register. A read of this register clears the status flags affected by transient conditions.

Reference Section 4.5 for details on the response for each status condition.

3.1.11.1

Unused Bits (UNUSED)

The unused bits have no impact on operation or performance. When read these bits may be ‘1’ or ‘0’.

3.1.11.2

Internal Data Error Flag (IDE)

The internal data error flag is set if a customer or OTP register data CRC fault or other internal fault is detected as defined in

Section 4.5.5. The internal data error flag is cleared by a read of the DEVSTAT register. If the error is associated with a CRC fault

in the writable register array, the fault will be re-asserted and will require a device reset to clear. If the error is associated with the

data stored in the fuse array, the fault will be re-asserted even after a device reset.

3.1.11.3

Device Initialization Flag (DEVINIT)

The device initialization flag is set during the interval between negation of internal reset and completion of internal device ini-

tialization. DEVINIT is cleared automatically. The device initialization flag is not affected by a read of the DEVSTAT register.

3.1.11.4

SPI MISO Data Mismatch Error Flag (MISOERR)

The MISO data mismatch flag is set when a MISO Data mismatch fault occurs as specified in Section 4.5.2. The MISOERR

flag is cleared by a read of the DEVSTAT register.

3.1.11.5

Offset Monitor Error Flags (OFF_X, OFFSET_Y)

The offset monitor error flags are set if the acceleration signal of the associated axis reaches the specified offset limit. The

offset monitor error flags are cleared by a read of the DEVSTAT register.

3.1.11.6

Device Reset Flag (DEVRES)

The device reset flag is set during device initialization following a device reset. The device reset flag is cleared by a read of

the DEVSTAT register.

Table 21. Threshold Register Value Examples

Axis Type

Programmed Thresholds

Positive Threshold

(g)

Negative Threshold

(g)

Range

(g)

Sensitivity

(LSB/g)

Positive

(Decimal)

Negative

(Decimal)

80

24

100

50

4.17

-2.08

80

24

255

0

10.625

Disabled

80

24

50

20

2.08

-0.83

80

24

150

75

6.25

-3.125

105.5

18.2

100

50

5.50

-2.75

105.5

18.2

255

0

14.0

Disabled

105.5

18.2

50

20

2.75

-1.10

105.5

18.2

150

75

8.24

-4.12

Table 22. Device Status Register

Location

Bit

Address

Register

76543210

$14

DEVSTAT

UNUSED

IDE

UNUSED

DEVINIT

MISOERR

OFF_Y

OFF_X

DEVRES