Provided by: freebsd-manpages_12.2-1_all bug


     lm75 — lm75 i2c digital temperature sensor driver


     device iic
     device iicbus
     device lm75


     The lm75 driver provides access to sensor data and configuration over the iicbus(4).

     It provides an easy and simple way to check the functionality of an i2c bus as it provides
     read and write access to the lm75 configuration register.

     The access to lm75 data is made via the sysctl(8) interface:

     dev.lm75.0.%desc: LM75 temperature sensor
     dev.lm75.0.%driver: lm75
     dev.lm75.0.%location: addr=0x49
     dev.lm75.0.%pnpinfo: name=lm750 compat=national,lm75
     dev.lm75.0.%parent: iicbus3
     dev.lm75.0.temperature: 27.1C
     dev.lm75.0.thyst: 75.0C
     dev.lm75.0.tos: 80.0C
     dev.lm75.0.faults: 1
     dev.lm75.0.mode: comparator
     dev.lm75.0.polarity: active-low
     dev.lm75.0.shutdown: 0

     dev.lm75.%d.temperature  Is the read-only value of the current temperature read by the

     dev.lm75.%d.thyst        Sets the hysteresis temperature.  Once the temperature gets over
                              the overtemperature shutdown value (tos) it needs to drop below the
                              hysteresis temperature to disable the output (interrupt) pin again.

     dev.lm75.%d.tos          Sets the overtemperature shutdown value.  Once the temperature gets
                              over this value the output pin will be enabled.  The way the output
                              (interrupt) pin works, depends on the mode configuration.

     dev.lm75.%d.faults       Is the number of faults that must occur consecutively to activate
                              the interrupt (output) pin.  It can be set to 1, 2, 4, and 6.

     dev.lm75.%d.mode         Sets the operation mode for the sensor interrupt pin.  It can be
                              set to 'comparator' (default) or 'interrupt'.

     dev.lm75.%d.polarity     Sets the polarity of the sensor interrupt pin.  It can be set to
                              'active-low' (default) or 'active-high'.  Please note that the
                              output pin is an open-drain output and it needs a proper pull-up
                              resistor to work.

     dev.lm75.%d.shutdown     When set to '1' it shuts down the sensor.  The temperature
                              conversion stops but the sensor remains with its i2c bus active,
                              i.e., it can be woken up by setting this option to '0' again.

     Please check the lm75 datasheet for more details.

     When used together with snmp_lm75(3) it allows the monitoring of lm75 temperature data over

     The lm75 driver supports both the low and the high resolution models.

     The low resolution model (lm75) provides a 9 bit output with the LSB representing 0.5C.

     The high resolution model (lm75a) provides an 11 bit output with the LSB representing

     The driver tries to auto-detect the lm75 model, but the detection of some lm75 clones may
     not work reliably.

     On a device.hints(5) based system, such as MIPS, these values are configurable for lm75:    Is the iicbus(4) you are attaching to.

     hint.lm75.%d.addr  Is the lm75 i2c address on the iicbus(4).

     On a FDT(4) based system, such as ARM, the DTS part for a lm75 device usually looks like:

     i2c {
             /* Properties describing the controller appear here. */
             lm750@49 {
                     compatible = "national,lm75";
                     reg = <0x49>;


     compatible  Should always be set to "national,lm75".

     reg         Indicates which 7-bit i2c address the lm75 is wired at.  lm75 temperature
                 sensors can be wired to 8 different addresses, allowing up to 8 sensors on the
                 same iicbus(4).


     snmp_lm75(3), fdt(4), iic(4), iicbus(4), sysctl(8)


     The lm75 driver first appeared in FreeBSD 11.0.


     The lm75 driver and this manual page were written by Luiz Otavio O Souza <>.