DS18S20 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS18S20

High Precision 1-Wire® Digital Thermometer

Dallas Semiconductor -> Maxim Integrated 

DS18S20

OPERATION – MEASURING TEMPERATURE

The core functionality of the DS18S20 is its direct-to-digital temperature sensor. The direct readout of

temperature data is 9 bits wide, equating to a resolution of 0.5°C; if higher resolution is desired, an

algorithm is described later in this section to achieve that need. Following the issuance of the Convert T

[44h] command, a temperature conversion is performed and the thermal data is stored in the scratchpad

memory in a 16-bit, sign-extended two’s complement format. The temperature information can be

retrieved over the 1-Wire interface by issuing a Read Scratchpad [BEh] command once the conversion

has been performed. The data is transferred over the 1-Wire bus, LSB first. The MSB of the temperature

register contains the “sign” (S) bit, denoting whether the temperature is positive or negative.

Table 2 describes the exact relationship of output data to measured. For Fahrenheit usage, a lookup table

or conversion routine must be used.

Temperature/Data Relationships Table 2

26 25 24 23 22 21 20 2-1 LSB

MSb

(unit = °C)

LSb

S S S S S S S S MSB

TEMPERATURE DIGITAL OUTPUT

(Binary)

+85°C

+125°C

+25.0°C

+0.5°C

0°C

-0.5°C

-25.0°C

-55°C

0000 0101 0101 0000

0000 0000 1111 1010

0000 0000 0011 0010

0000 0000 0000 0001

0000 0000 0000 0000

1111 1111 1111 1111

1111 1111 1100 1110

1111 1111 1001 0010

DIGITAL

OUTPUT

(Hex)

0550h*

00FAh

0032h

0001h

0000h

FFFFh

FFCEh

FF92h

*The power on reset register value is +85°C

Higher resolutions may be obtained by the following procedure. First, read the temperature,

COUNT_REMAIN, and COUNT_PER_C registers from the scratchpad. Truncate the 0.5°C bit (the

LSB) from the temperature value. This value is TEMP_READ. The actual temperature may then be

calculated by using the following:

TEMPERATURE = TEMP _ READ − 0.25 + COUNT _ PER _ C − COUNT _ REMAIN

COUNT _ PER _ C

OPERATION – ALARM SIGNALING

After the DS18S20 has performed a temperature conversion, the temperature value is compared to the

trigger values stored in TH and TL. Since these registers are 8–bit only, the 0.5°C bit is ignored for

comparison. The most significant bit of TH or TL directly corresponds to the sign bit of the 16–bit

temperature register. If the result of a temperature measurement is higher than TH or lower than TL, an

alarm flag inside the device is set. This flag is updated with every temperature measurement. As long as

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