[linux-block.git] / Documentation / hwmon / lm77.rst

Kernel driver lm77
==================

Supported chips:

  * National Semiconductor LM77

    Prefix: 'lm77'

    Addresses scanned: I2C 0x48 - 0x4b

    Datasheet: Publicly available at the National Semiconductor website

	       http://www.national.com/


Author: Andras BALI <drewie@freemail.hu>

Description
-----------

The LM77 implements one temperature sensor. The temperature
sensor incorporates a band-gap type temperature sensor,
10-bit ADC, and a digital comparator with user-programmable upper
and lower limit values.

The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and
critical (temp1_crit.) It also implements an hysteresis mechanism which
applies to all 3 limits. The relative difference is stored in a single
register on the chip, which means that the relative difference between
the limit and its hysteresis is always the same for all 3 limits.

This implementation detail implies the following:

* When setting a limit, its hysteresis will automatically follow, the
  difference staying unchanged. For example, if the old critical limit
  was 80 degrees C, and the hysteresis was 75 degrees C, and you change
  the critical limit to 90 degrees C, then the hysteresis will
  automatically change to 85 degrees C.
* All 3 hysteresis can't be set independently. We decided to make
  temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are
  read-only. Setting temp1_crit_hyst writes the difference between
  temp1_crit_hyst and temp1_crit into the chip, and the same relative
  hysteresis applies automatically to the low and high limits.
* The limits should be set before the hysteresis.
Commit	Line	Data
7f15b664 M	1	Kernel driver lm77
	2	==================
	3
	4	Supported chips:
b04f2f7d	5
7f15b664	6	* National Semiconductor LM77
b04f2f7d	7
7f15b664	8	Prefix: 'lm77'
b04f2f7d	9
7f15b664	10	Addresses scanned: I2C 0x48 - 0x4b
b04f2f7d	11
7f15b664	12	Datasheet: Publicly available at the National Semiconductor website
b04f2f7d MCC	13
	14	http://www.national.com/
	15
7f15b664 M	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
50bf4650 GR	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:
b04f2f7d	34
50bf4650 GR	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.