DS18S20-PAR データシートの表示（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS18S20-PAR

1-Wire® Parasite-Power Digital Thermometer

Dallas Semiconductor -> Maxim Integrated 

DS18S20-PAR

16 (10h). After reading the scratchpad, the TEMP_READ value is obtained by truncating the 0.5°C bit

(bit 0) from the temperature data (see Figure 3). The extended resolution temperature can then be

calculated using the following equation:

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

COUNT _ PER _ C

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”.

TEMPERATURE REGISTER FORMAT Figure 3

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

LS Byte

26

25

24

23

22

21

20

2-1

bit 15

bit 14

bit 13

bit 12

bit 11

bit 10

bit 9

bit 8

MS Byte S

S

S

S

S

S

S

S

TEMPERATURE/DATA RELATIONSHIP Table 2

TEMPERATURE DIGITAL OUTPUT DIGITAL OUTPUT

(Binary)

(Hex)

+85.0°C*

0000 0000 1010 1010

00AAh

+25.0°C

0000 0000 0011 0010

0032h

+0.5°C

0000 0000 0000 0001

0001h

0°C

0000 0000 0000 0000

0000h

-0.5°C

1111 1111 1111 1111

FFFFh

-25.0°C

1111 1111 1100 1110

FFCEh

-55.0°C

1111 1111 1001 0010

FF92h

*The power-on reset value of the temperature register is +85°C

OPERATION – ALARM SIGNALING

After the DS18S20-PAR performs a temperature conversion, the temperature value is compared to the

user-defined two’s complement alarm trigger values stored in the 1-byte TH and TL registers (see Figure

4). The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for

negative numbers S = 1. The TH and TL registers are nonvolatile (EEPROM) so they will retain data

when the device is powered down. TH and TL can be accessed through bytes 2 and 3 of the scratchpad as

explained in the MEMORY section of this datasheet.

TH AND TL REGISTER FORMAT Figure 4

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

S

26

25

25

25

22

21

20

Only bits 8 through 1 of the temperature register are used in the TH and TL comparison since TH and TL

are 8-bit registers. If the result of a temperature measurement is higher than TH or lower than TL, an

alarm condition exists and an alarm flag is set inside the DS18S20-PAR. This flag is updated after every

temperature measurement; therefore, if the alarm condition goes away, the flag will be turned off after the

next temperature conversion.

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