DS9490B datasheet(13/44 Pages) MAXIM

13 / 44 page

High-Temperature Logger iButton with 8KB

Data-Log Memory

______________________________________________________________________________________

Latest Temperature Conversion Result Register

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

BYTE

020Ch

TRL

020Dh

T10

TRH

Temperature Conversion

The DS1922E’s temperature range begins at +15°C

and ends at +140°C. Temperature values are repre-

sented as an 8- or 16-bit unsigned binary number with

a resolution of 0.5°C in 8-bit mode and 0.0625°C in

16-bit mode.

The higher temperature byte TRH is always valid. In

16-bit mode, only the three highest bits of the lower

byte TRL are valid. The five lower bits all read 0. TRL is

undefined if the device is in 8-bit temperature mode. An

out-of-range temperature reading is indicated as 00h or

0000h when too cold and FFh or FFE0h when too hot.

With TRH and TRL representing the decimal equivalent

of a temperature reading, the temperature value is cal-

culated as:

ϑ(°C) = TRH/2 + 14 + TRL/512 (16-bit mode,

TLFS = 1, see address 0213h)

ϑ(°C) = TRH/2 + 14 (8-bit mode, TLFS = 0,

see address 0213h)

This equation is valid for converting temperature read-

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

read from the Latest Temperature Conversion Result

To specify the temperature alarm thresholds, the previ-

ous equations are resolved to:

TALM = 2 x

ϑ(°C) - 28

Because the temperature alarm threshold is only one

byte, the resolution or temperature increment is limited

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

decimal format before it can be written to one of the

Temperature Alarm Threshold registers (Low Alarm

address 0208h; High Alarm address 0209h).

Independent of the conversion mode (8- or 16-bit), only

the most significant byte of a temperature conversion is

used to determine whether an alarm is generated.

Table 1. Temperature Conversion Examples

TRH

TRL

MODE

HEX

DECIMAL

HEX

DECIMAL

(°C)

8-Bit

54h

—

56.0

8-Bit

17h

—

25.5

16-Bit

54h

00h

56.0000

16-Bit

17h

60h

25.6875

Table 2. Temperature Alarm Threshold Examples

TALM

(°C)

HEX

DECIMAL

65.5

67h

103

30.0

20h

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