Rainbow-electronics DS2422 Manuel d'utilisateur télécharger pdf (Page 13)

DS2422

13 of 48

SAMPLE RATE

The content of the Sample Rate Register (addresses 0206h, 0207h) specifies the time elapse (in seconds if EHSS

= 1, or minutes if EHSS = 0) between two temperature/data logging events. The sample rate may be any value

from 1 to 16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging

events is 1 second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and

the longest time is 273.05 hours (sample rate = 3FFFh). The EHSS bit is located in the RTC Control Register at

address 0212h. It is important that the user sets the EHSS bit accordingly while setting the Sample Rate register. A

sample rate of 0000h is not valid and must be avoided under all circumstances. This causes the device to enter

into an undefined state, requiring a power-on reset and restore of the trim settings to recover.

Sample Rate Register Bitmap

ADDR b7 b6 b5 b4 b3 b2 b1 b0

0206h Sample Rate Low

0207h 0 0 Sample Rate High

During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be

written to 1.

TEMPERATURE CONVERSION

The DS2422 can measure temperatures from -40°C to +85°C. Temperature values are represented as an 8- or 16-

bit unsigned binary number with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.

The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte

TRL are valid. The five lower bits all read zero. 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.

Latest Temperature Conversion Result Register Bitmap

ADDR b7 b6 b5 b4 b3 b2 b1 b0

020Ch T2 T1 T0 0 0 0 0 0

TRL

020Dh T10 T9 T8 T7 T6 T5 T4 T3

TRH

With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is

calculated as

J(°C) = TRH/2 - 41 + TRL/512 (16 bit mode, TLFS = 1, see address 0213h)

J(°C) = TRH/2 - 41 (8 bit mode, TLFS = 0, see address 0213h)

This equation is valid for converting temperature readings stored in the datalog memory as well as for data read

from the Latest Temperature Conversion Result Register.

To specify the temperature alarm thresholds, the equation above needs to be resolved to

TALM = 2 * J (°C) + 82

Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5°C.

The TALM value needs to be converted into hexadecimal 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 will be generated.

Temperature Conversion Examples

Mode

TRH

hex decimal

TRL

hex decimal

J(°C)

8-bit 54h

—— 1.0

8-bit 17h

— — -29.5

16-bit 54h

00h

1.000

16-bit 17h

60h

-29.3125

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 47 48

Commentaires sur ces manuels

Pas de commentaire

Rainbow-electronics DS2422 Manuel d'utilisateur Page 13

Commentaires sur ces manuels

Produits connexes et manuels pour Panneau de contrôle Rainbow-electronics DS2422