ADIS16203SLASHPCBZ datasheet(16/28 Pages) AD

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ADIS16203

Rev. 0 | Page 16 of 28

The ALM_MAG1 control register used in controlling the Alarm 1

function has two roles. The first role is to store the value with which

the output data variable is compared against to discern if an alarm

condition exists. The second role is to identify whether the alarm

should be active for excursions above or below the alarm limit. If 1 is

written to Bit 15 of the ALM_MAG1 control register, the alarm is

active for excursions extending above a given limit. If 0 is written to

Bit 15, the alarm is active for excursions dropping below the given

limit. The comparison value contained within the ALM_MAG1

control register is located within the lower 14 bits.

The monitored output register establishes the format of the

14-bit data space in the ALM_MAG1 and ALM_MAG2 registers. For

example, setting the alarm to monitor INCL_OUT sets the data

format to a 14-bit, twos complement number, which carries a bit

weight of 0.025°.

Use caution when monitoring the temperature output register for the

alarm conditions. Here, the negative temperature scale factor results

in the greater than and less than selections requiring reverse logic.

Setting Bit 11 in the ALM_CTRL register establishes the mode of

operation: threshold or rate of change (ROC). When the ROC

function is enabled, the comparison of the output data variable is

against the ALM_MAG1 level averaged over the number of samples

as identified in the ALM_SMPL1 control register. This acts to create

a comparison of (Δ units/Δ time) or the derivative of the output data

variable against a predefined slope.

The versatility built into the alarm function allows the user to adapt

to several applications. For example, in the case of monitoring twos

complement variables, Bit 15 within the ALM_MAG1 control register

can allow for the detection of negative excursions below a fixed level.

In addition, the Alarm 1 and Alarm 2 functions can be set to monitor

the same variable that allows the user to discern if an output variable

remains within a predefined window.

Another potential ROC application is to monitor slowly changing

outputs in the inclination level. With the addition of the alarm hard-

ware functionality, the ADIS16203 can be left to run independently

of the main processor and interrupt the system only when an alarm

condition occurs. Conversely, the alarm condition can be monitored

through the routine polling of any one of the seven data output registers.

Bits 4 and 5 in the ALM_CTRL register establishes whether

ALM_MAG1 and ALM_MAG2 are compared with filtered or

unfiltered data.

ALM_MAG1 Register Definition

Address

Default1

Format2

Access

0x21, 0x20

0x0000

N/A

R/W

1 Default is valid only until the first register write cycle.

2 Format is established by source of monitored data

The ALM_MAG1 register contains the threshold level for

Alarm 1. The contents of this register are nonvolatile.

Table 11. ALM_MAG1 Bit Designations

Bit

Description

Greater than Active Alarm Bit.

1: Alarm is active for an output greater than

ALM_MAG1 register setting.

0: Alarm is active for an output less than

ALM_MAG1 register setting.

Not used.

13:0

Data Bits. This number can be either twos complement

or straight binary. The format is set by the value being

monitored by this function.

ALM_SMPL1 Register Definition

Address

Default1

Format

Access

0x25, 0x24

0x0000

Binary

R/W

1 Default is valid only until the first register write cycle.

The ALM_SMPL1 register contains the sample period information

for Alarm 1, when it is set for ROC alarm monitoring. The ROC

alarm function averages the change in the output variable over the

specified number of samples and compares this change directly

to the values specified in the ALM_MAG1 register. The contents

of this register are nonvolatile.

Table 12. ALM_SMPL1 Bit Designations

Bit

Description

15:8

Not used

7:0

Data bits

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