Preliminary Technical Data

ADIS16220

Rev. PrE | Page 11 of 16

READING DATA FROM THE CAPTURE BUFFER

Initiate a manual capture command by setting GLOB_CMD[11]

= 1 (DIN = 0xBF08). Wait for DIO1 to go high and then low

before using the SPI port. When the capture is complete, the

first data samples load into the CAPT_BUFx registers and

0x0000 loads into the index pointer (CAPT_PNTR). The index

pointer determines which data samples load into the CAPT_BUFx

registers. For example, writing 0x0138 to the CAPT_PNTR

in the buffer memory to load into the CAPT_BUFx registers.

CAPT_BUFA

ACCELERATION

CAPTURE

BUFFER

CAPT_PNTR

1023

0

Figure 14. Acceleration Capture Buffer Structure and Operation;

CAPT_BUF1 (AIN1) and CAPT_BUF2 (AIN2) Use Similar Structures

Table 9. CAPT_PNTR Bits Descriptions

Bit

Description (Default = 0x0000)

[15:10]

Not used

[9:0]

Data bits

The index pointer automatically increments with a CAPT_BUFA,

CAPT_BUF1, or CAPT_BUF2 read command. In the master

processor firmware, the loop may appear similar to the following:

Data(0) = spi_reg_read(0x14)

For n = 0 to 1023

Data(n) = spi_reg_read(0x14);

n = n + 1;

end

Output Data Format

The CAPT_BUFA and CAPT_PEAKA registers use a 14-bit, twos

complement format to accommodate acceleration in both direc-

tions (positive and negative). In addition to the acceleration data,

a capture event also produces analog input data (CAPT_BUF1,

CAPT_BUF2), power supply data (CAPT_SUPPLY), temperature

data (CAPT_TEMP), the peak acceleration level (CAPT_PEAKA)

and the peak analog input levels (CAPT_PEAK1, CAPT_PEAK2)

in the captured data.

Table 10. Capture Output Register Formats

Register

Bits

Format

Scale

CAPT_SUPPLY

12

Binary, 0 V = 0 LSB

1.22 mV

CAPT_TEMP

12

Binary, 25°C = 1278 LSB

−0.47°C

CAPT_BUFA,

CAPT_PEAKA

16

Twos complement

19.073 mg

CAPT_BUF1,

CAPT_BUF2,

CAPT_PEAK1,

CAPT_PEAK2

16

Twos complement

305.18 μV

Table 11. Acceleration Data Format

Output (Binary)

Hex

LSB

Acceleration

0000 1110 0101 0001

0x0E56

+3670

+70 g

0000 0000 0000 0001

0x0001

+1

+0.019073 g

0000 0000 0000 0000

0x0000

0

0

1111 1111 1111 1111

0xFFFF

−1

−0.019073 g

1111 0001 1010 1101

0xF1AA

−3670

−70 g

Table 12. Analog Input Data Format

Output (Binary)

Hex

LSB

Level (mV)

0000 1100 1100 1101

0x0CCD

+3277

VDD/2 + 1000

0000 0000 0000 0001

0x0001

+1

VDD/2 + 0.305

0000 0000 0000 0000

0x0000

0

VDD/2

1111 1111 1111 1111

0xFFFF

−1

VDD/2 − 0.305

1111 0011 0011 0010

0xF332

-3277

VDD/2 − 1000

where CAPT_SUPPLY = 2703 LSB.

Temperature Equation

Temperature = (1278 − CAPT_TEMP) × 0.47°C/LSB +

25°C.

For example, when CAPT_TEMP = 1331, the result is 0.1°C.

CAPTURE MODE CONFIGURATION

The CAPT_CTRL register provides three different options for

triggering a data capture: manual, automatic, and event. It also

offers an option for placing the device in a low power, shutdown

mode in between capture events. This setting adds approximately

2.3 ms to the total capture time relationship:

)

flash

with

(

2

1024

184

,

97

1

516

.

0

)

flash

no

(

2

1024

184

,

97

1

014

.

0

_

_

CNT

AVG

C

CNT

AVG

C

T

T

















Table 13. CAPT_CTRL Bit Descriptions

Bit

Description

(Default = 0x0020)

[15:7]

Not used

[6]

Automatically store capture buffers to flash upon alarm

trigger (1 = enabled)

[5:4]

Pre-event capture length

00 = 64 samples

01 = 128 samples

10 = 256 samples

11 = 512 samples

[3:2]

Capture mode

00 = manual: use GLOB_CMD[11] to start capture

01 = automatic: use CAPT_PRD[9:0] to set capture period

10 = event: continuously monitor data for the conditions

set in ALM_CTRL, ALM_MAGA, ALM_MAG1, and ALM_MAG2.

11 = not used

[1]

Power-down between capture events

1 = enabled, which requires CS toggle to wake up

[0]

Not used