Functional description, Lm81 – Rainbow Electronics LM81 User Manual
Page 19
Functional Description
(Continued)
8.0 TEMPERATURE MEASUREMENT SYSTEM
The LM81 temperature sensor and ADC produce 9-bit or
12-bit two’s-complement temperature data. A digital com-
parator
compares
the
temperature
data
to
the
user-programmable High, Low, Critical setpoints and Hyster-
esis values.
8.1 Temperature Data Format
Temperature data can be read from the Temperature, T
HIGH
setpoint, T
HIHYST
setpoint, T
LOW
setpoint, T
C
setpoint and
T
HYST
Offset registers; and written to the T
HIGH
setpoint,
T
HIHYST
, T
LOW
setpoint, T_CRIT setpoint and T
HYST
offset
registers. T
HIGH
setpoint, T
LOW
setpoint, T_CRIT setpoint
temperature data is represented by an 8-bit, two’s comple-
ment word with an LSB (Least Significant Bit) equal to 1˚C:
Temperature
Digital Output
Binary
Hex
+125˚C
0111 1101
7Dh
+25˚C
0001 1001
19h
+1.0˚C
0000 0001
01h
+0˚C
0000 0000
00h
−1.0˚C
1111 1111
FFh
−25˚C
1110 0111
E7h
−40˚C
1101 1000
D8h
By default Temperature Register data is represented by a
9-bit two’s complement digital word with the LSB having a
resolution of 0.5˚C:
Temperature
Digital Output
Binary
Hex
+125˚C
0 1111 1010
0 FAh
+25˚C
0 0011 0010
0 32h
+1.5˚C
0 0000 0011
0 03h
+0˚C
0 0000 0000
0 00h
−0.5˚C
1 1111 1111
1 FFh
−25˚C
1 1100 1110
1 CEh
−40˚C
1 1011 0000
1 B0h
In the extended mode temperature Register data can also be
represented by a 12-bit two’s complement digital word with
an LSB of 0.0625˚C:
Temperature
Digital Output
Binary
Hex
+125˚C
0111 1100 0000
7 D0h
+25˚C
0001 1001 0000
1 90h
+1.0˚C
0000 0001 0000
0 10h
+0.0625˚C
0000 0000 0001
0 01h
0˚C
0000 0000 0000
0 00h
−0.0625˚C
1111 1111 1111
F FFh
−1.0˚C
1111 1111 0000
F F0h
−25˚C
1110 0111 0000
E 70h
−40˚C
1101 1000 0000
D 80h
T
HYST
Offset temperature data is represented by a 3-bit word
with an LSB (Least Significant Bit) equal to 1˚C.
DS100072-24
(Non-Linear Scale for Clarity)
FIGURE 9. 9-bit Temperature-to-Digital Transfer
Function
DS100072-27
(Non-Linear Scale for Clarity)
FIGURE 10. 12-bit Temperature-to-Digital Transfer
Function
LM81
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