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HTU21(4)	       FreeBSD Kernel Interfaces Manual		      HTU21(4)

NAME
     htu21 -- driver for HTU21D	and compatible temperature and humidity	sen-
     sors

SYNOPSIS
     To	compile	this driver into the kernel, place the following lines in your
     kernel configuration file:

	   device htu21
	   device iicbus

     Alternatively, to load the	driver as a module at boot time, place the
     following line in loader.conf(5):

	   htu21_load="YES"

DESCRIPTION
     The htu21 driver provides temperature and relative	humidity readings over
     I2C bus for the supported sensors:
     +o	 HTU21D
     +o	 SHT21
     +o	 Si7021

     The htu21 driver reports data via sysctl(8) entries in the	device's node
     in	the sysctl(8) tree:

     temperature  The temperature, in hundredths of Kelvin.

     humidity	  The relative humidity, in hundredths of a percent.

     crc_errors	  The number of	CRC errors in reading the measurements from
		  the device.

     power	  The good power indication.  This can be useful with battery
		  powered sensors.

     heater	  The built-in heater control.	The heater can be used for
		  testing and for recovery from	saturation after high humid-
		  ity.

     hold_bus	  Whether the sensor should hold SCL low while performing the
		  measurement.	Normally, the sensor releases the bus and
		  NACKs	all accessed until the measurement is completed.  The
		  hold mode may	be useful in mult-master environments.

     On	an FDT(4) based	system the following properties	must be	set:

     compatible	 Must be set to	"meas,htu21".

     reg	 The I2C address of htu21.  Although, it is hard-wired to 0x40
		 (7-bit) on all	supported sensors.

     The DTS part for a	htu21 device usually looks like:

     / {

	     ...
	     htu21d {
		     compatible	= "meas,htu21";
		     reg = <0x40>;
	     };
     };

SEE ALSO
     fdt(4), iicbus(4),	sysctl(8)

HISTORY
     The htu21 driver and this manual page was written by Andriy Gapon
     <avg@FreeBSD.org>.

BUGS
     There is no way to	control	the measurment resolution.

     Some sensor variants do not provide a serial number or use	an incompati-
     ble format.  The htu21 driver does	not distinguish	those variants and may
     complain about incorrect serial number checksum.

FreeBSD	13.0		       January 19, 2021			  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | BUGS

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