DS1925 datasheet(14/46 Pages) MAXIM

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Alarm Status

The fastest way to determine whether a programmed

temperature threshold was exceeded during a mission is

through reading the Alarm Status register. In a networked

environment that contains multiple DS1925 devices, the

devices that encountered an alarm can quickly be identi-

fied by means of the Conditional Search ROM command

(see the 1-Wire ROM Function Commands section).

The temperature alarm only occurs if enabled (see the

Temperature Sensor Alarm). The BOR alarm is always

enabled. See Table 13 for the bitmap and Table 14 for the

bit descriptions. There is only read access to this register.

Bits 6:4 have no function; they always read 1. Bits 3:2 have

no function with the DS1925; they always read 0. The alarm

status bits are cleared simultaneously when the XPC Clear

Memory function is invoked. See the Memory and Control

Function Commands for details.

General Status

The information in the General Status register tells the

host computer whether a mission-related command was

executed successfully. Individual status bits indicate

whether the DS1925 is performing a mission, waiting for a

temperature alarm to trigger the logging of data, or wheth-

er the data from the latest mission has been cleared. See

Table 15 for the bitmap. There is only read access to this

are normally 0’s for typical operation but change to 1’s

to indicate if the register pages are a backup copy and

represent the last state recorded at the start of a mission.

Mission Start Delay Counter

The content of the Mission Start Delay Counter register

tells how many minutes have to expire from the time a

mission was started until the first measurement of the

mission takes place (SUTA = 0), or until the device starts

testing the temperature for a temperature alarm (SUTA

= 1). The Mission Start Delay is stored as an unsigned

24-bit integer number. If the start delay is non-zero and

the SUTA bit is set to 1, first the delay has to expire before

the device starts testing for temperature alarms to begin

logging data. See Table 17 for the register bitmap. During

a mission, there is only read access to these registers.

For a typical mission, the Mission Start Delay Counter is

0. If a mission is too long for a single DS1925 to store all

readings at the selected sample rate, one can use several

devices and set the Mission Start Delay for the second

device to start recording as soon as the memory of the

first device is full, and so on.

Mission Timestamp

The Mission Timestamp register indicates the date and

time of the start of the mission. The time of the first tem-

perature sample of the mission can be computed by add-

ing the Mission Timestamp with the Mission Start Delay

Counter. The Mission Timestamp register indicates the

date and time of the first temperature sample of the mis-

sion. There is only read access to the Mission Timestamp

Table 13. Alarm Status Register Bitmap

Table 14. Alarm Status Register Bit Descriptions

DS1925

iButton High-Capacity Temperature Logger

with 122KB Data-Log Memory

www.maximintegrated.com

Maxim Integrated │ 14

ADDR

0214h

BOR

THF

TLF

BIT

NAME

FUNCTION

BOR

Battery On Reset Alarm. If this bit reads 1, the device has performed a power-on-reset or battery-fail

event. See the Revision History section for BOR behavior by version.

THF

Temperature High Alarm Flag. If this bit reads 1, there was at least one temperature conversion

during a mission revealing a temperature equal to or higher than the value in the Temperature High

Alarm register. A forced conversion can affect the THF bit. This bit can also be set with the initial

alarm in the SUTA = 1 mode.

TLF

Temperature Low Alarm Flag. If this bit reads 1, there was at least one temperature conversion

during a mission revealing a temperature equal to or lower than the value in the Temperature Low

Alarm Register. A forced conversion can affect the TLF bit. This bit can also be set with the initial

alarm in the SUTA = 1 mode.

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