Rainbow-electronics DS1821 Manual de usuario descargar pdf (Pagina 5)

DS1821

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configuration register to determine when the conversion status: DONE = 0 ― conversion in progress,

DONE = 1 ― conversion complete. The DONE bit does not provide conversion status in continuous

conversion mode since measurements are constantly in progress (i.e., DONE will always be 0).

TEMPERATURE, T

and T

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

TEMPERATURE/DATA RELATIONSHIP Table 2

TEMPERATURE DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+125°C* 0111 1101 7Dh

+85°C 0101 0101 55h

+25°C 0001 1001 19h

0°C 0000 0000 00h

-1°C 1111 1111 FFh

-25°C 1110 0111 E7h

-55°C 1100 1001 C9h

HIGH-RESOLUTION TEMPERATURE READINGS

The user can calculate temperature values with higher than 8-bit resolution using the data remaining in

the counter and slope accumulator when the temperature conversion is complete. To do this the user must

first read the temperature from the 8-bit temperature register. This value is called TEMP_READ in the

high-resolution equation (see Eq. 1). The 9-bit counter value must then be obtained by issuing the Read

Counter [A0h] command. This value is the count remaining in the counter at the end of the gate period

and is called COUNT_REMAIN in Eq. 1. Next the Load Counter [41h] command must be issued, which

loads the 9-bit slope accumulator value into the counter register. The slope accumulator value (called

COUNT_PER_C in Eq. 1) can then be read from the counter by again issuing the Read Counter [A0h]

command. The slope accumulator value is called “COUNT_PER_C” because it represents the number of

counts needed for an accurate measurement at a given temperature (i.e., the counts per degree C). The

high-resolution temperature can then be calculated using Eq. 1:

Eq. 1) TEMPERATURE = TEMP_READ

−

0.5 +

CPERCOUNT

REMAINCOUNTCPERCOUNT

)___( −

Additional information about high-resolution temperature calculations can be found in Application Note

105: “High Resolution Temperature Measurement with Dallas Direct-to-Digital Temperature Sensors”.

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Rainbow-electronics DS1821 Manual de usuario Pagina 5