ADIS16204

Rev. 0 | Page 15 of 24

GLOBAL COMMANDS

The ADIS16204 provides global commands, which simplify

many common operations. The COMMAND register provides

command bits for each function. Writing a 1 to the assigned

command bit exercises its function. The flash update copies the

contents of all nonvolatile registers into their assigned, nonvolatile,

flash memory locations. This process takes approximately 50 ms

and requires a power supply that is within the specified operating

range. After waiting the appropriate time for the flash update to

complete, verify successful completion by reading the STATUS

register (Flash update error = zero, if successful). If the flash

update was not successful, reading this error bit will accomplish

two things: (1) alert system processor to try again, and (2) clear

the error flag, which is required for flash memory access.

The software reset command restarts the internal processor,

which loads all registers with the contents in their flash memory

locations. The DAC data latch command loads the contents of

AUX_DAC into the DAC latches. Because the AUX_DAC

contents must be updated one byte at a time, this command

ensures a stable DAC output voltage during updates.

Calibration Commands

The autonull command provides a simple method for removing

offset from the sensor outputs. This command takes separate

64-sample measurements for each axis (X, Y), then loads the

opposite value into each axis’ offset null register. The accuracy

of this operation depends on zero force or motion during the

64-sample timeframe. The factory calibration restore sets the

scale and offset null registers (XACCL_NULL, for example)

back to their default values. For more information on

ADIS16204 calibration, see the Calibration section.

Event Capture Commands

The COMMAND register provides four different functions that

simplify the process of using the event capture function. The

reset-capture pointer function sets the contents of the capture

pointer to its initial value of 0x0001. The clear capture flash,

clear capture buffer, and capture flash copy commands are self-

descriptive. The capture flash copy takes approximately 120 ms

to complete and serves the purpose of copying the capture buffer

into nonvolatile flash memory. See the Alarm Detection and

Event Capture section for more information.

Table 8. COMMAND Register Definition

Address

Default

Format

Access

0x3F, 0x3E

N/A

N/A

W only

Table 9. COMMAND Bit Descriptions

Bit

Description

15:11

Not used

10

Reset capture pointer (set CAPT_PNTR to 0x0001)

9

Clear capture flash (nonvolatile back-up)

8

Clear capture buffer (SRAM)

7

Software reset

6

Copy capture buffer to nonvolatile flash

5

Clear peak output registers, (reset them to 0x0000)

4

Clear status register (reset all bits to 0)

3

Flash update—saves nonvolatile register settings

2

DAC data latch

1

Factory calibration restore

0

Autonull

CALIBRATION

In addition to the factory calibration, the ADIS16204 provides

a user configurable calibration for systems that require accuracy

improvements. For example, a vehicle system may require better

resolution to separate a minor bump from a hard brake event.

In cases like this, the ADIS16204 provides configuration registers

that adjust both offset and sensitivity (gain) on both X- and

Y-axes. The following relationship describes the calibration

function:

y = mx + b

where:

y is the calibrated output data.

m is the scale factor multiplier [XACCL_SCALE/YACCL_SCALE].

x is the precalibration data.

b is the offset adder [XACCL_NULL/YACCL_NULL].

Assuming zero offset and nominal scale factor (sensitivity),

the offset adjustment range for the X-axis is ±35.054 g and

±17.527 g for the Y-axis. Assuming zero offset, the scale factor

adjustment range is 0 to 2.

Table 10. XACCL_NULL Register Definition

Address

Scale1

Default

Format

Access

0x11, 0x10

17.125 mg

0x0000

Twos

complement

R/W

Table 11. YACCL_NULL Register Definition

Address

Scale1

Default

Format

Access

0x13, 0x12

8.407 mg

0x0000

Twos

complement

R/W

Table 12. XACCL_SCALE Register Definition

Address

Scale1

Default2

Format

Access

0x15, 0x14

0.0488%

0x0800

Binary

R/W