DS18B20-PAR
resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1 and 0 are undefined. Table 2 gives
examples of digital output data and the corresponding temperature reading for 12-bit resolution
conversions.
TEMPERATURE REGISTER FORMAT
Figure 3
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
LS Byte
MS Byte
2
3
bit 15
2
2
bit 14
2
1
bit 13
2
0
bit 12
2
-1
bit 11
2
-2
bit 10
2
-3
bit 9
2
-4
bit 8
S
S
S
S
S
2
6
2
5
2
4
TEMPERATURE/DATA RELATIONSHIP
Table 2
TEMPERATURE
+85°C*
+25.0625°C
+10.125°C
+0.5°C
0°C
-0.5°C
-10.125°C
-25.0625°C
-55°C
DIGITAL OUTPUT
(Binary)
DIGITAL OUTPUT
(Hex)
0000 0101 0101 0000
0000 0001 1001 0001
0000 0000 1010 0010
0000 0000 0000 1000
0000 0000 0000 0000
1111 1111 1111 1000
1111 1111 0101 1110
1111 1110 0110 1111
1111 1100 1001 0000
0550h
0191h
00A2h
0008h
0000h
FFF8h
FF5Eh
FE6Fh
FC90h
*The power-on reset value of the temperature register is +85°C
OPERATION – ALARM SIGNALING
After the DS18B20-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 T
H
and T
L
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 T
H
and T
L
registers are nonvolatile (EEPROM) so they will retain data
when the device is powered down. T
H
and T
L
can be accessed through bytes 2 and 3 of the scratchpad as
explained in the MEMORY section of this datasheet.
T
H
AND T
L
REGISTER FORMAT
Figure 4
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
S
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Only bits 11 through 4 of the temperature register are used in the T
H
and T
L
comparison since T
H
and T
L
are 8-bit registers. If the result of a temperature measurement is higher than or equal to T
H
or lower than
or equal to T
L
, an alarm condition exists and an alarm flag is set inside the DS18B20-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.
4 of 19
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