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diff --git a/Documentation/hwmon/lm77.rst b/Documentation/hwmon/lm77.rst new file mode 100644 index 000000000000..4ed3fe6b999a --- /dev/null +++ b/Documentation/hwmon/lm77.rst @@ -0,0 +1,45 @@ +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. |