Description¶

The LM73 is a digital temperature sensor. All temperature values aregiven in degrees Celsius.

Measurement Resolution Support¶

The LM73 supports four resolutions, defined in terms of degrees C perLSB: 0.25, 0.125, 0.0625, and 0.3125. Changing the resolution modeaffects the conversion time of the LM73’s analog-to-digital converter.From userspace, the desired resolution can be specified as a function ofconversion time via the ‘update_interval’ sysfs attribute for thedevice. This attribute will normalize ranges of input values to themaximum times defined for the resolution in the datasheet.

Resolution	Conv. Time	Input Range
(C/LSB)	(msec)	(msec)
0.25	14	0..14
0.125	28	15..28
0.0625	56	29..56
0.03125	112	57..infinity

The following examples show how the ‘update_interval’ attribute can beused to change the conversion time:

$ echo 0 > update_interval$ cat update_interval14$ cat temp1_input24250$ echo 22 > update_interval$ cat update_interval28$ cat temp1_input24125$ echo 56 > update_interval$ cat update_interval56$ cat temp1_input24062$ echo 85 > update_interval$ cat update_interval112$ cat temp1_input24031

As shown here, the lm73 driver automatically adjusts any user input for‘update_interval’ via a step function. Reading back the‘update_interval’ value after a write operation will confirm theconversion time actively in use.

Mathematically, the resolution can be derived from the conversion timevia the following function:

g(x) = 0.250 * [log(x/14) / log(2)]

where ‘x’ is the output from ‘update_interval’ and ‘g(x)’ is theresolution in degrees C per LSB.

Alarm Support¶

The LM73 features a simple over-temperature alarm mechanism. Thisfeature is exposed via the sysfs attributes.

The attributes ‘temp1_max_alarm’ and ‘temp1_min_alarm’ are flagsprovided by the LM73 that indicate whether the measured temperature haspassed the ‘temp1_max’ and ‘temp1_min’ thresholds, respectively. Thesevalues _must_ be read to clear the registers on the LM73.