SCA61T Series

VTI Technologies Oy

Subject to changes

11/18

www.vti.fi

Doc. nr. 8261900

Rev.A

•

data transfer out from MISO starts with the falling edge of SCK immediately after the last bit of

the SPI command is sampled in on the rising edge of SCK

•

maximum SPI clock frequency is 500kHz

•

maximum data transfer speed for RDAX is 5300 samples per sec / channel

The SPI command can be either an individual command or a combination of command and data.

In the case of combined command and data, the input data follows uninterruptedly the SPI

command and the output data is shifted out parallel with the input data.

The SPI interface uses an 8-bit instruction (or command) register. The list of commands is given in

Table below.

Command

Name

Command

Format

Description:

MEAS

00000000

Measure mode (normal operation mode after power on)

RWTR

00001000

Read and write temperature data register

RDSR

00001010

Read status register

RLOAD

00001011

Reload NV data to memory output register

STX

00001110

Activate Self test for X-channel

RDAX

00010000

Read X-channel acceleration through SPI

Measure mode (MEAS)

is standard operation mode after power-up. During normal operation, the

MEAS command is the exit command from Self test.

Read temperature data register (RWTR)

reads temperature data register during normal

operation without effecting the operation. Temperature data register is updated every 150 µs. The

load operation is disabled whenever the CSB signal is low, hence CSB must stay high at least 150

µs prior the RWTR command in order to guarantee correct data. The data transfer is presented in

Figure below. The data is transferred MSB first. In normal operation, it does not matter what data is

written into temperature data register during the RWTR command and hence writing all zeros is

recommended.

7

6

5

4

3

2

1

0

7

6

5

4

3

2

1

0

CS B

SC K

MIS O

MO S I

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

HIG H IM PE DA N C E

CO M M A N D

DA T A IN

DA T A OU T

Figure 10.

Command and 8 bit temperature data transmission over the SPI

Self test for X-channel (STX)

activates the self test function for the X-channel (Channel 1). The

Internal charge pump is activated and a high voltage is applied to the X-channel acceleration

sensor element electrode. This causes the electrostatic force that deflects the beam of the sensing

element and simulates the acceleration to the positive direction. The self-test is de-activated by

giving the MEAS command.

Read X-channel acceleration (RDAX)

accesses the AD converted X-channel acceleration signal

stored in acceleration data register X.

During normal operation, acceleration data registers are reloaded every 150 µs. The load

operation is disabled whenever the CSB signal is low, hence CSB must stay high at least 150 µs

prior the RDAX command in order to guarantee correct data. Data output is an 11-bit digital word

that is fed out MSB first and LSB last.