1 Kernel driver lm77 1 Kernel driver lm77
2 ================== 2 ==================
3 3
4 Supported chips: 4 Supported chips:
5 5
6 * National Semiconductor LM77 6 * National Semiconductor LM77
7 7
8 Prefix: 'lm77' 8 Prefix: 'lm77'
9 9
10 Addresses scanned: I2C 0x48 - 0x4b 10 Addresses scanned: I2C 0x48 - 0x4b
11 11
12 Datasheet: Publicly available at the Natio 12 Datasheet: Publicly available at the National Semiconductor website
13 13
14 http://www.national.com/ 14 http://www.national.com/
15 15
16 16
17 Author: Andras BALI <drewie@freemail.hu> 17 Author: Andras BALI <drewie@freemail.hu>
18 18
19 Description 19 Description
20 ----------- 20 -----------
21 21
22 The LM77 implements one temperature sensor. Th 22 The LM77 implements one temperature sensor. The temperature
23 sensor incorporates a band-gap type temperatur 23 sensor incorporates a band-gap type temperature sensor,
24 10-bit ADC, and a digital comparator with user 24 10-bit ADC, and a digital comparator with user-programmable upper
25 and lower limit values. 25 and lower limit values.
26 26
27 The LM77 implements 3 limits: low (temp1_min), 27 The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and
28 critical (temp1_crit.) It also implements an h 28 critical (temp1_crit.) It also implements an hysteresis mechanism which
29 applies to all 3 limits. The relative differen 29 applies to all 3 limits. The relative difference is stored in a single
30 register on the chip, which means that the rel 30 register on the chip, which means that the relative difference between
31 the limit and its hysteresis is always the sam 31 the limit and its hysteresis is always the same for all 3 limits.
32 32
33 This implementation detail implies the followi 33 This implementation detail implies the following:
34 34
35 * When setting a limit, its hysteresis will au 35 * When setting a limit, its hysteresis will automatically follow, the
36 difference staying unchanged. For example, i 36 difference staying unchanged. For example, if the old critical limit
37 was 80 degrees C, and the hysteresis was 75 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 38 the critical limit to 90 degrees C, then the hysteresis will
39 automatically change to 85 degrees C. 39 automatically change to 85 degrees C.
40 * All 3 hysteresis can't be set independently. 40 * All 3 hysteresis can't be set independently. We decided to make
41 temp1_crit_hyst writable, while temp1_min_hy 41 temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are
42 read-only. Setting temp1_crit_hyst writes th 42 read-only. Setting temp1_crit_hyst writes the difference between
43 temp1_crit_hyst and temp1_crit into the chip 43 temp1_crit_hyst and temp1_crit into the chip, and the same relative
44 hysteresis applies automatically to the low 44 hysteresis applies automatically to the low and high limits.
45 * The limits should be set before the hysteres 45 * The limits should be set before the hysteresis.
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