Documentation/hwmon/lm77.rst

   1 Kernel driver lm77
   2 ==================
   3
   4 Supported chips:
   5
   6   * National Semiconductor LM77
   7
   8     Prefix: 'lm77'
   9
  10     Addresses scanned: I2C 0x48 - 0x4b
  11
  12     Datasheet: Publicly available at the National Semiconductor website
  13
  14                http://www.national.com/
  15
  16
  17 Author: Andras BALI <drewie@freemail.hu>
  18
  19 Description
  20 -----------
  21
  22 The LM77 implements one temperature sensor. The temperature
  23 sensor incorporates a band-gap type temperature sensor,
  24 10-bit ADC, and a digital comparator with user-programmable upper
  25 and lower limit values.
  26
  27 The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and
  28 critical (temp1_crit.) It also implements an hysteresis mechanism which
  29 applies to all 3 limits. The relative difference is stored in a single
  30 register on the chip, which means that the relative difference between
  31 the limit and its hysteresis is always the same for all 3 limits.
  32
  33 This implementation detail implies the following:
  34
  35 * When setting a limit, its hysteresis will automatically follow, the
  36   difference staying unchanged. For example, if the old critical limit
  37   was 80 degrees C, and the hysteresis was 75 degrees C, and you change
  38   the critical limit to 90 degrees C, then the hysteresis will
  39   automatically change to 85 degrees C.
  40 * All 3 hysteresis can't be set independently. We decided to make
  41   temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are
  42   read-only. Setting temp1_crit_hyst writes the difference between
  43   temp1_crit_hyst and temp1_crit into the chip, and the same relative
  44   hysteresis applies automatically to the low and high limits.
  45 * The limits should be set before the hysteresis.