0001 Kernel driver lm73
0002 ==================
0003
0004 Supported chips:
0005
0006 * Texas Instruments LM73
0007
0008 Prefix: 'lm73'
0009
0010 Addresses scanned: I2C 0x48, 0x49, 0x4a, 0x4c, 0x4d, and 0x4e
0011
0012 Datasheet: Publicly available at the Texas Instruments website
0013
0014 https://www.ti.com/product/lm73
0015
0016
0017 Author: Guillaume Ligneul <guillaume.ligneul@gmail.com>
0018
0019 Documentation: Chris Verges <kg4ysn@gmail.com>
0020
0021
0022 Description
0023 -----------
0024
0025 The LM73 is a digital temperature sensor. All temperature values are
0026 given in degrees Celsius.
0027
0028 Measurement Resolution Support
0029 ------------------------------
0030
0031 The LM73 supports four resolutions, defined in terms of degrees C per
0032 LSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution mode
0033 affects the conversion time of the LM73's analog-to-digital converter.
0034 From userspace, the desired resolution can be specified as a function of
0035 conversion time via the 'update_interval' sysfs attribute for the
0036 device. This attribute will normalize ranges of input values to the
0037 maximum times defined for the resolution in the datasheet.
0038
0039 ============= ============= ============
0040 Resolution Conv. Time Input Range
0041 (C/LSB) (msec) (msec)
0042 ============= ============= ============
0043 0.25 14 0..14
0044 0.125 28 15..28
0045 0.0625 56 29..56
0046 0.03125 112 57..infinity
0047 ============= ============= ============
0048
0049 The following examples show how the 'update_interval' attribute can be
0050 used to change the conversion time::
0051
0052 $ echo 0 > update_interval
0053 $ cat update_interval
0054 14
0055 $ cat temp1_input
0056 24250
0057
0058 $ echo 22 > update_interval
0059 $ cat update_interval
0060 28
0061 $ cat temp1_input
0062 24125
0063
0064 $ echo 56 > update_interval
0065 $ cat update_interval
0066 56
0067 $ cat temp1_input
0068 24062
0069
0070 $ echo 85 > update_interval
0071 $ cat update_interval
0072 112
0073 $ cat temp1_input
0074 24031
0075
0076 As shown here, the lm73 driver automatically adjusts any user input for
0077 'update_interval' via a step function. Reading back the
0078 'update_interval' value after a write operation will confirm the
0079 conversion time actively in use.
0080
0081 Mathematically, the resolution can be derived from the conversion time
0082 via the following function:
0083
0084 g(x) = 0.250 * [log(x/14) / log(2)]
0085
0086 where 'x' is the output from 'update_interval' and 'g(x)' is the
0087 resolution in degrees C per LSB.
0088
0089 Alarm Support
0090 -------------
0091
0092 The LM73 features a simple over-temperature alarm mechanism. This
0093 feature is exposed via the sysfs attributes.
0094
0095 The attributes 'temp1_max_alarm' and 'temp1_min_alarm' are flags
0096 provided by the LM73 that indicate whether the measured temperature has
0097 passed the 'temp1_max' and 'temp1_min' thresholds, respectively. These
0098 values _must_ be read to clear the registers on the LM73.
