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LM75(4)                FreeBSD Kernel Interfaces Manual                LM75(4)

     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

     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

     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 sensor.

     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

     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

     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 SNMP.

     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 0.125C.

     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, like 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, like ARM, the DTS part for a lm75 device
     usually looks like:

     i2c {


             lm750 {
                     compatible = "national,lm75";
                     i2c-address = <0x49>;


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

     i2c-address      The i2c-address property indicates which 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
     <[email protected]>.

FreeBSD 11.1-RELEASE-p4          May 11, 2014          FreeBSD 11.1-RELEASE-p4
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