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OW_TEMP(4)		    Kernel Interfaces Manual		    OW_TEMP(4)

NAME
       ow_temp -- Dallas Semiconductor 1-Wire Temperature sensor

SYNOPSIS
       device ow_temp

DESCRIPTION
       The ow_temp module supports many	of the 1-Wire temperature sensors.

       The  sensor  is	read  periodically  and	 the  results  returned	 via a
       sysctl(3) as described below.

HARDWARE
       These temperature sensors are supported by the ow_temp driver:
       DS1820	 1-Wire	Digital	Thermometer
       DS18S20	 High-Precision	1-Wire Digital Thermometer
       DS18B20	 Programmable Resolution 1-Wire	Digital	Thermometer
       DS1822	 Econo 1-Wire Digital Thermometer
       DS1825	 Programmable Resolution 1-Wire	Digital	Thermometer with 4-bit
		 ID
       MAX31820	 1-Wire, Parasite-Power, Ambient Temperature Sensor

       The driver supports Family codes	0x10, 0x22, 0x28, and 0x3b.

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

       temperature
		   The last temperature	read, in milli-Kelvin.

       badcrc	   The	number	of  CRC	errors in reading the temperature form
		   the device.	Some CRC errors	 are  to  be  expected.	  High
		   rates  of  CRC  errors, however, generally indicate a noisy
		   environment,	cabling	issues,	or too	many  devices  on  the
		   bus.

       badread	   The number of times a non-CRC error was encountered reading
		   the	temperature from the card.  This type of error is very
		   rare.

       reading_interval
		   The time, in	ticks, between successive reads	of the sensor.

       parasite	   This	item is	non-zero when the device  is  connected	 using
		   its	parasitic  power  mode.	 It can	also indicate a	wiring
		   error.

       Temperatures are	reported in milli-Kelvin, even though the absolute ac-
       curacy is around	0.2 degrees for	the good devices and around  1	degree
       for  cheaper  devices.	The devices report in steps of 0.0625 degrees.
       The driver preserves the	precision of the device's measurements in  its
       sysctl(8) reports.  These devices often have a much higher relative ac-
       curacy and repeatability	than their absolute accuracy.  This makes them
       well suited for control loops that strive for stability and become pos-
       sible if	the full precision is preserved.

SEE ALSO
       ow(4), owc(4), sysctl(8), owll(9), own(9)

LEGAL
       1-Wire is a registered trademark	of Maxim Integrated Products, Inc.

HISTORY
       The ow_temp driver first	appeared in FreeBSD 11.0.

AUTHORS
       The  ow_temp  device driver and this manual page	were written by	Warner
       Losh.

BUGS
       The parasitic mode of the devices does not work.	 It  requires  support
       from the	owc(4) driver that is unimplemented.

       The ID bits from	the DS1825 are not recognized or reported.

       The type	of the device is not reported via sysctl(8).

       Alarm  mode  is	not  supported.	 It is not possible to set the low and
       high alarm temperatures.

       There is	no way to write	to the EEPROM.

       "Convert	Temperature" requests are sent directly	to the device.	 There
       is  no way to use the broadcast ability of the 1-Wire bus to do all the
       conversions in parallel.

       It is not possible to set the precision on those	devices	 that  support
       it.

       The  time to convert is fixed at	1 second, even though some devices are
       faster.

       There is	no character device to supply a	stream of readings to  a  pro-
       gram.   Programs	 interested in the temperature must poll the sysctl to
       get the temperature.

FreeBSD	13.2			 July 20, 2015			    OW_TEMP(4)

NAME | SYNOPSIS | DESCRIPTION | HARDWARE | SYSCTL | SEE ALSO | LEGAL | HISTORY | AUTHORS | BUGS

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