About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / w1 / slaves / w1_therm

Custom Search

Based on kernel version 4.1. Page generated on 2015-06-28 12:15 EST.

1	Kernel driver w1_therm
2	====================
4	Supported chips:
5	  * Maxim ds18*20 based temperature sensors.
6	  * Maxim ds1825 based temperature sensors.
8	Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
11	Description
12	-----------
14	w1_therm provides basic temperature conversion for ds18*20 devices.
15	supported family codes:
16	W1_THERM_DS18S20	0x10
17	W1_THERM_DS1822		0x22
18	W1_THERM_DS18B20	0x28
19	W1_THERM_DS1825		0x3B
21	Support is provided through the sysfs w1_slave file.  Each open and
22	read sequence will initiate a temperature conversion then provide two
23	lines of ASCII output.  The first line contains the nine hex bytes
24	read along with a calculated crc value and YES or NO if it matched.
25	If the crc matched the returned values are retained.  The second line
26	displays the retained values along with a temperature in millidegrees
27	Centigrade after t=.
29	Parasite powered devices are limited to one slave performing a
30	temperature conversion at a time.  If none of the devices are parasite
31	powered it would be possible to convert all the devices at the same
32	time and then go back to read individual sensors.  That isn't
33	currently supported.  The driver also doesn't support reduced
34	precision (which would also reduce the conversion time).
36	The module parameter strong_pullup can be set to 0 to disable the
37	strong pullup, 1 to enable autodetection or 2 to force strong pullup.
38	In case of autodetection, the driver will use the "READ POWER SUPPLY"
39	command to check if there are pariste powered devices on the bus.
40	If so, it will activate the master's strong pullup.
41	In case the detection of parasite devices using this command fails
42	(seems to be the case with some DS18S20) the strong pullup can
43	be force-enabled.
44	If the strong pullup is enabled, the master's strong pullup will be
45	driven when the conversion is taking place, provided the master driver
46	does support the strong pullup (or it falls back to a pullup
47	resistor).  The DS18b20 temperature sensor specification lists a
48	maximum current draw of 1.5mA and that a 5k pullup resistor is not
49	sufficient.  The strong pullup is designed to provide the additional
50	current required.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.