1 Kernel driver lm73 1 Kernel driver lm73
2 ================== 2 ==================
3 3
4 Supported chips: 4 Supported chips:
5 5
6 * Texas Instruments LM73 6 * Texas Instruments LM73
7 7
8 Prefix: 'lm73' 8 Prefix: 'lm73'
9 9
10 Addresses scanned: I2C 0x48, 0x49, 0x4a, 0 10 Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e
11 11
12 Datasheet: Publicly available at the Texas 12 Datasheet: Publicly available at the Texas Instruments website
13 13
14 https://www.ti.com/product/lm73 14 https://www.ti.com/product/lm73
15 15
16 16
17 Author: Guillaume Ligneul <guillaume.ligneul@gm 17 Author: Guillaume Ligneul <guillaume.ligneul@gmail.com>
18 18
19 Documentation: Chris Verges <kg4ysn@gmail.com> 19 Documentation: Chris Verges <kg4ysn@gmail.com>
20 20
21 21
22 Description 22 Description
23 ----------- 23 -----------
24 24
25 The LM73 is a digital temperature sensor. All 25 The LM73 is a digital temperature sensor. All temperature values are
26 given in degrees Celsius. 26 given in degrees Celsius.
27 27
28 Measurement Resolution Support 28 Measurement Resolution Support
29 ------------------------------ 29 ------------------------------
30 30
31 The LM73 supports four resolutions, defined in 31 The LM73 supports four resolutions, defined in terms of degrees C per
32 LSB: 0.25, 0.125, 0.0625, and 0.3125. Changin 32 LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode
33 affects the conversion time of the LM73's anal 33 affects the conversion time of the LM73's analog-to-digital converter.
34 From userspace, the desired resolution can be 34 From userspace, the desired resolution can be specified as a function of
35 conversion time via the 'update_interval' sysf 35 conversion time via the 'update_interval' sysfs attribute for the
36 device. This attribute will normalize ranges 36 device. This attribute will normalize ranges of input values to the
37 maximum times defined for the resolution in th 37 maximum times defined for the resolution in the datasheet.
38 38
39 ============= ============= ============ 39 ============= ============= ============
40 Resolution Conv. Time Input Range 40 Resolution Conv. Time Input Range
41 (C/LSB) (msec) (msec) 41 (C/LSB) (msec) (msec)
42 ============= ============= ============ 42 ============= ============= ============
43 0.25 14 0..14 43 0.25 14 0..14
44 0.125 28 15..28 44 0.125 28 15..28
45 0.0625 56 29..56 45 0.0625 56 29..56
46 0.03125 112 57..infinity 46 0.03125 112 57..infinity
47 ============= ============= ============ 47 ============= ============= ============
48 48
49 The following examples show how the 'update_in 49 The following examples show how the 'update_interval' attribute can be
50 used to change the conversion time:: 50 used to change the conversion time::
51 51
52 $ echo 0 > update_interval 52 $ echo 0 > update_interval
53 $ cat update_interval 53 $ cat update_interval
54 14 54 14
55 $ cat temp1_input 55 $ cat temp1_input
56 24250 56 24250
57 57
58 $ echo 22 > update_interval 58 $ echo 22 > update_interval
59 $ cat update_interval 59 $ cat update_interval
60 28 60 28
61 $ cat temp1_input 61 $ cat temp1_input
62 24125 62 24125
63 63
64 $ echo 56 > update_interval 64 $ echo 56 > update_interval
65 $ cat update_interval 65 $ cat update_interval
66 56 66 56
67 $ cat temp1_input 67 $ cat temp1_input
68 24062 68 24062
69 69
70 $ echo 85 > update_interval 70 $ echo 85 > update_interval
71 $ cat update_interval 71 $ cat update_interval
72 112 72 112
73 $ cat temp1_input 73 $ cat temp1_input
74 24031 74 24031
75 75
76 As shown here, the lm73 driver automatically a 76 As shown here, the lm73 driver automatically adjusts any user input for
77 'update_interval' via a step function. Readin 77 'update_interval' via a step function. Reading back the
78 'update_interval' value after a write operatio 78 'update_interval' value after a write operation will confirm the
79 conversion time actively in use. 79 conversion time actively in use.
80 80
81 Mathematically, the resolution can be derived 81 Mathematically, the resolution can be derived from the conversion time
82 via the following function: 82 via the following function:
83 83
84 g(x) = 0.250 * [log(x/14) / log(2)] 84 g(x) = 0.250 * [log(x/14) / log(2)]
85 85
86 where 'x' is the output from 'update_interval' 86 where 'x' is the output from 'update_interval' and 'g(x)' is the
87 resolution in degrees C per LSB. 87 resolution in degrees C per LSB.
88 88
89 Alarm Support 89 Alarm Support
90 ------------- 90 -------------
91 91
92 The LM73 features a simple over-temperature al 92 The LM73 features a simple over-temperature alarm mechanism. This
93 feature is exposed via the sysfs attributes. 93 feature is exposed via the sysfs attributes.
94 94
95 The attributes 'temp1_max_alarm' and 'temp1_mi 95 The attributes 'temp1_max_alarm' and 'temp1_min_alarm' are flags
96 provided by the LM73 that indicate whether the 96 provided by the LM73 that indicate whether the measured temperature has
97 passed the 'temp1_max' and 'temp1_min' thresho 97 passed the 'temp1_max' and 'temp1_min' thresholds, respectively. These
98 values _must_ be read to clear the registers o 98 values _must_ be read to clear the registers on the LM73.
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