DS1925 datasheet(12/46 Pages) MAXIM

12 / 46 page

With TRH and TRL representing the decimal equivalent

of a temperature reading, calculate the temperature value

as:

(°C) = TRH/2 - 41+ TRL/512 (16-bit mode, TLFS = 1,

see address 0213h)

(°C) = TRH/2 - 41

(8-bit mode, TLFS = 0,

see address 0213h)

This equation is valid for converting temperature readings

stored in the data-log memory as well as for data read

from the Latest Temperature Conversion Result register.

The “- 41” applies to the DS1925.

To specify the temperature alarm thresholds, the previous

equation needs to be resolved to:

TALM = 2 x J (°C) + 82

where “+ 82” applies to the DS1925.

Because the temperature alarm threshold is only 1 byte,

the resolution or temperature increment is limited to

0.5°C. The TALM value needs to be converted into hexa-

decimal format before it can be written to one of the tem-

perature alarm threshold registers (

low alarm address

0208h; high alarm address 0209h). Independent of the

conversion mode (8-bit or 16-bit), only the most significant

byte of a temperature conversion is used to determine

whether an alarm is generated.

Temperature Sensor Alarm

The DS1925 has two Temperature Alarm Threshold regis-

ters (address 0208h, 0209h) to store values, which deter-

mine whether a critical temperature has been reached. A

temperature alarm is generated if the device measures an

alarming temperature

and the alarm signaling is enabled.

The ETLA and ETHA bits that enable the temperature

alarm are located in the Temperature Sensor Control

there is only read access to this register. Bits 7:2 have no

function. They always read 0 and cannot be written to 1.

The temperature alarm flags TLF and THF are found in

the Alarm Status register at address 0214h.

Table 6. Temperature Alarm Threshold Examples

Table 7. Temperature Sensor Control Register Bitmap

Table 8. Temperature Sensor Control Register Bit Descriptions

DS1925

iButton High-Capacity Temperature Logger

with 122KB Data-Log Memory

www.maximintegrated.com

Maxim Integrated │ 12

J (°C)

TALM (DS1925)

HEX

DECIMAL

25.5

85h

133

-10.0

3Eh

ADDR

0210h

ETHA

ETLA

BIT

NAME

FUNCTION

ETHA

Enable Temperature High Alarm. This bit controls whether during a mission the temperature high alarm

flag (THF) may be set, if a temperature conversion results in a value equal to or higher than the value in

the Temperature High Alarm Threshold Register. If ETHA is 1, temperature high alarms are enabled. If

ETHA is 0, temperature high alarms are not generated.

ETLA

Enable Temperature Low Alarm. This bit controls whether during a mission the temperature low alarm

flag (TLF) may be set, if a temperature conversion results in a value equal to or lower than the value

in the Temperature Low Alarm Threshold register. If ETLA is 1, temperature low alarms are enabled. If

ETLA is 0, temperature low alarms are not generated.

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