CMA3000-D0X Series

VTI Technologies Oy

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www.vti.fi

Doc.Nr. 8281000.12

Rev. 0.12

2

Reset and power up, Operation Modes, HW functions and Clock

2.1

Reset and power up

The CMA3000 has internal power-on reset circuit. It releases the internal reset-signal once the

power supplies will be within the specified range.

After releasing the internal reset, the CMA3000 will read configuration and calibration data from the

non-volatile memory to volatile registers. Then the CMA3000 will make parity check to the read

memory content. The STATUS register's PERR-bit="0" shows successful memory read operation.

Device can be externally reset by writing the sequence 02h, 0Ah, 04h into the RSTR-register.

2.2

Power Down mode

The CMA3000-D0X enters the power down mode by default after power-on reset and initialization

of the volatile registers. PD can also be set by writing MODE[2:0] = 000b (or MODE[2:0] = 111b) to

CTRL register.

Output registers will keep their content in the power down mode.

2.3

Measurement Mode

2.3.1

Description

The CMA3000-D0X is set to a measurement mode by writing MODE[2:0] = 0XXb to CTRL register.

Data will be reliable in the output registers after the product specific turn-on time.

Default sample rate is 400 Hz (MODE[2:0] = 010b). Other data rates are 100 Hz (MODE[2:0] =

001b) and 40 Hz (MODE[2:0] = 011b).

Table 2. CMA3000-D0X measurement ranges and output sample rates

Measurement range

Output sample rates

2 g

400 Hz, 100 Hz

8 g

400 Hz, 100 Hz, 40 Hz

INT-pin gives an interrupt by default when new data is available.

2.3.2

Usage

Acceleration data can be read from data output registers DOUTX, DOUTY and DOUTZ. See

section 2.6 for INT-pin configuration details.

2.4

Motion Detection Mode

2.4.1

Description

In MD mode the device works at 10 Hz sample rate and the fixed measurement range is 8 g. Signal

is band pass filtered and fed to threshold level programmable digital comparator and a configurable

trigger function. Filtered signal is also available at output registers.

The device can be configured to switch automatically into the measurement mode with highest

sampling rate (400Hz) after motion is detected. The measurement range used will be defined by

G_RANGE bit.

Nominal BPF's -3 dB high-pass frequency is 1.3 Hz and -3 dB low-pass frequency is 3.8 Hz. See

Figure 3 below.