SCA3000 datasheet(12/43 Pages) VTI

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SCA3000 Series

VTI Technologies Oy

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Doc.Nr. 8257300A.07

Rev.A.07

2.5

Ring Buffer

2.5.1

Description

The SCA3000's Ring Buffer is a 192 acceleration data samples long (64 samples of 11 bit three

axis data) internal memory to relax the real-time operation requirements of the host processor. The

following parameters are configurable:

Each measurement axis can be individually disabled. If measurement data from e.g. Y-axis

is not needed, available memory can be used for X- and Z-axis data.

Buffer data length can be changed from 11 to 8 bits. In 8-bit mode, data can be read out

using shorter read sequence.

Ring buffer's input sample rate can be the same as the sensor's data rate or divided by 2

or 4. When the divider is e.g. 2, only every 2

nd acceleration data will be stored.

The Interrupt condition, when enabled, can be selected between two: interrupt in INT-pin

occurs when the buffer is 50% or 75% full.

2.5.2

Usage

The ring buffer can be enabled by setting BUF_EN bit in MODE register to "1". After enabling the

buffer, acceleration data can be read from BUF_DATA register using decrement register read,

which is described in section 4.1.3.2 for SPI and 4.2.1.3 for I

2C interface.

Each measurement axis can be individually disabled by setting corresponding bits in BUF_X_EN,

BUF_Y_EN and BUF_Z_EN in OUT_CTRL register to "0".

Output data length can be changed from 11 bits to 8 bits by setting bit BUF_8BIT in MODE register

to "1". See section 3.3 for bit level descriptions.

The count of available data samples in output ring buffer can be read from BUF_COUNT register.

2C.

Data shift out order is X,Y,Z. In 11 bit mode two bytes must be read to get all 11 bits out. In that

case, the MSB byte is 1

st. Examples:

11 bits data length, X&Y&Z axis enabled:

X1_MSB, X1_LSB, Y1_MSB, Y1_LSB, Z1_MSB, Z1_LSB, X2_MSB, X2_LSB, ... latest

Z_LSB

11 bits data length, Y&Z axis enabled:

Y1_MSB, Y1_LSB, Z1_MSB, Z1_LSB, Y2_MSB, Y2_LSB, Z2_MSB, Z2_LSB, Y3_MSB,

Y3_LSB, ..., latest Z_LSB

8 bits data length, all axis enabled:

X1, Y1, Z1, X2, Y2, Z2,..., latest Z

8 bits data length, X&Z axis enabled:

X1, Z1, X2, Z2, X3, Z3, ..., latest Z

8 bits data length, Z axis enabled:

Z1, Z2, Z3, ... , latest Z

See section 2.7 for interrupt functionality details.

Acceleration data is available in X_LSB, X_MSB, Y_LSB, Y_MSB, Z_LSB and Z_MSB when the

ring buffer is enabled.

2.5.2.1

Overflow condition

Overflow is detected from data ring buffer in same way as from the output registers. See section

2.2.2.1 for details.

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