linux/Documentation/hwmon/lm80
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   1Kernel driver lm80
   2==================
   3
   4Supported chips:
   5  * National Semiconductor LM80
   6    Prefix: 'lm80'
   7    Addresses scanned: I2C 0x28 - 0x2f
   8    Datasheet: Publicly available at the National Semiconductor website
   9               http://www.national.com/
  10  * National Semiconductor LM96080
  11    Prefix: 'lm96080'
  12    Addresses scanned: I2C 0x28 - 0x2f
  13    Datasheet: Publicly available at the National Semiconductor website
  14               http://www.national.com/
  15
  16Authors:
  17        Frodo Looijaard <frodol@dds.nl>,
  18        Philip Edelbrock <phil@netroedge.com>
  19
  20Description
  21-----------
  22
  23This driver implements support for the National Semiconductor LM80.
  24It is described as a 'Serial Interface ACPI-Compatible Microprocessor
  25System Hardware Monitor'. The LM96080 is a more recent incarnation,
  26it is pin and register compatible, with a few additional features not
  27yet supported by the driver.
  28
  29The LM80 implements one temperature sensor, two fan rotation speed sensors,
  30seven voltage sensors, alarms, and some miscellaneous stuff.
  31
  32Temperatures are measured in degrees Celsius. There are two sets of limits
  33which operate independently. When the HOT Temperature Limit is crossed,
  34this will cause an alarm that will be reasserted until the temperature
  35drops below the HOT Hysteresis. The Overtemperature Shutdown (OS) limits
  36should work in the same way (but this must be checked; the datasheet
  37is unclear about this). Measurements are guaranteed between -55 and
  38+125 degrees. The current temperature measurement has a resolution of
  390.0625 degrees; the limits have a resolution of 1 degree.
  40
  41Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
  42triggered if the rotation speed has dropped below a programmable limit. Fan
  43readings can be divided by a programmable divider (1, 2, 4 or 8) to give
  44the readings more range or accuracy. Not all RPM values can accurately be
  45represented, so some rounding is done. With a divider of 2, the lowest
  46representable value is around 2600 RPM.
  47
  48Voltage sensors (also known as IN sensors) report their values in volts.
  49An alarm is triggered if the voltage has crossed a programmable minimum
  50or maximum limit. Note that minimum in this case always means 'closest to
  51zero'; this is important for negative voltage measurements. All voltage
  52inputs can measure voltages between 0 and 2.55 volts, with a resolution
  53of 0.01 volt.
  54
  55If an alarm triggers, it will remain triggered until the hardware register
  56is read at least once. This means that the cause for the alarm may
  57already have disappeared! Note that in the current implementation, all
  58hardware registers are read whenever any data is read (unless it is less
  59than 2.0 seconds since the last update). This means that you can easily
  60miss once-only alarms.
  61
  62The LM80 only updates its values each 1.5 seconds; reading it more often
  63will do no harm, but will return 'old' values.
  64
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