46 lines
1.6 KiB
ReStructuredText
46 lines
1.6 KiB
ReStructuredText
Kernel driver lm77
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==================
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Supported chips:
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* National Semiconductor LM77
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Prefix: 'lm77'
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Addresses scanned: I2C 0x48 - 0x4b
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Datasheet: Publicly available at the National Semiconductor website
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http://www.national.com/
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Author: Andras BALI <drewie@freemail.hu>
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Description
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-----------
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The LM77 implements one temperature sensor. The temperature
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sensor incorporates a band-gap type temperature sensor,
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10-bit ADC, and a digital comparator with user-programmable upper
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and lower limit values.
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The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and
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critical (temp1_crit.) It also implements an hysteresis mechanism which
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applies to all 3 limits. The relative difference is stored in a single
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register on the chip, which means that the relative difference between
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the limit and its hysteresis is always the same for all 3 limits.
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This implementation detail implies the following:
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* When setting a limit, its hysteresis will automatically follow, the
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difference staying unchanged. For example, if the old critical limit
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was 80 degrees C, and the hysteresis was 75 degrees C, and you change
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the critical limit to 90 degrees C, then the hysteresis will
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automatically change to 85 degrees C.
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* All 3 hysteresis can't be set independently. We decided to make
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temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are
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read-only. Setting temp1_crit_hyst writes the difference between
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temp1_crit_hyst and temp1_crit into the chip, and the same relative
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hysteresis applies automatically to the low and high limits.
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* The limits should be set before the hysteresis.
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