18B20 查看數據表（PDF） - Maxim Integrated
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18B20 Datasheet PDF : 22 Pages
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Figure 2. Temperature Register Format
DS18B20
LS BYTE
MS BYTE
BIT 7
23
BIT 15
S
BIT 6
22
BIT 14
S
BIT 5
21
BIT 13
S
BIT 4
20
BIT 12
S
BIT 3
2-1
BIT 11
S
BIT 2
2-2
BIT 10
26
BIT 1
2-3
BIT 9
25
BIT 0
2-4
BIT 8
24
S = SIGN
Table 1. Temperature/Data Relationship
TEMPERATURE (°C)
+125
DIGITAL OUTPUT
(BINARY)
0000 0111 1101 0000
+85*
+25.0625
+10.125
0000 0101 0101 0000
0000 0001 1001 0001
0000 0000 1010 0010
+0.5
0000 0000 0000 1000
0
0000 0000 0000 0000
-0.5
1111 1111 1111 1000
-10.125
-25.0625
-55
1111 1111 0101 1110
1111 1110 0110 1111
1111 1100 1001 0000
*The power-on reset value of the temperature register is +85°C.
DIGITAL OUTPUT
(HEX)
07D0h
0550h
0191h
00A2h
0008h
0000h
FFF8h
FF5Eh
FE6Fh
FC90h
OPERATION—ALARM SIGNALING
After the DS18B20 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 3).
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.
Figure 3. TH and TL Register Format
BIT 7
S
BIT 6
26
BIT 5
25
BIT 4
24
BIT 3
23
BIT 2
22
BIT 1
21
BIT 0
20
Only bits 11 through 4 of the temperature register are used in the TH and TL comparison since TH and TL
are 8-bit registers. If the measured temperature is lower than or equal to TL or higher than or equal to TH,
an alarm condition exists and an alarm flag is set inside the DS18B20. 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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