LM80 National Semiconductor, LM80 Datasheet - Page 17

• Manufacturer Part Number: LM80
• Description: Serial Interface ACPI-Compatible Microprocessor System Hardware Monitor
• Manufacturer: National Semiconductor

Functional Description
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 Register data can also be represented by a
12-bit two’s complement digital word with a LSB of 0.0625˚C:
The 8 MSBs of the Temperature reading can be found at
Value RAM address 28 h. The remainder of the Temperature
reading can be found in the OS Configuration/Temperature
Resolution Register bits 7-4. In 9-bit format bit 7 is the only
valid bit.
Temperature
Temperature
+0.0625˚C
−0.0625˚C
+125˚C
+125˚C
+1.5˚C
−0.5˚C
+1.0˚C
−1.0˚C
+25˚C
−25˚C
−55˚C
+25˚C
−25˚C
−55˚C
+0˚C
0˚C
0111 1100 0000
0001 1001 0000
0000 0001 0000
0000 0000 0001
0000 0000 0000
1111 1111 1111
1111 1111 0000
1110 0111 0000
1100 1001 0000
0 1111 1010
0 0011 0010
0 0000 0011
0 0000 0000
1 1111 1111
1 1100 1110
1 1001 0010
Binary
Binary
Digital Output
Digital Output
(Continued)
1 CEh
0 FAh
1 FFh
0 32h
0 03h
0 00h
1 92h
7 D0h
F FFh
F F0h
E 70h
C 90h
1 90h
0 10h
0 01h
Hex
Hex
00h
17
7.2 Temperature Interrupts
There are four Value RAM WATCHDOG limits for the Tem-
perature reading that affect the INT and OS outputs of the
LM80. They are: Hot Temperature Limit, Hot Temperature
Hysteresis Limit, OS Limit, OS Hysteresis Limit. There are
three interrupt modes of operation: “One-Time Interrupt”
mode, “Default Interrupt” mode, and “Comparator Mode”.
The OS output of the LM80 can be programmed for
“One-Time Interrupt” mode and “Comparator” mode. INT can
be programmed for “Default Interrupt” mode and “One-Time”
Interrupt.
“Default Interrupt mode” operates in the following way: Ex-
ceeding T
definitely until reset by reading Interrupt Status Register 1 or
cleared by the INT_Clear bit in the Configuration register.
Once an Interrupt event has occurred by crossing T
reset, an Interrupt will occur again once the next temperature
conversion has completed. The interrupts will continue to oc-
cur in this manner until the temperature goes below T
at which time the Interrupt output will automatically clear.
“One-Time Interrupt” mode operates in the following way:
Exceeding T
definitely until reset by reading Interrupt Status Register 1 or
cleared by the INT_Clear bit in the Configuration register.
Once an Interrupt event has occurred by crossing T
reset, an Interrupt will not occur again until the temperature
goes below T
“Comparator” mode operates in the following way: Ex-
ceeding T
will remain Low until the temperature goes below T
the temperature goes below T
os
hot
hot
causes the OS output to go Low (default). OS
causes an Interrupt that will remain active in-
hot hyst
causes an Interrupt that will remain active in-
.
os
, OS will go High.
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os
hot
hot
hot hyst
. Once
, then
, then
,