1Kernel driver w1_therm
2====================
3
4Supported chips:
5  * Maxim ds18*20 based temperature sensors.
6  * Maxim ds1825 based temperature sensors.
7
8Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
9
10
11Description
12-----------
13
14w1_therm provides basic temperature conversion for ds18*20 devices, and the
15ds28ea00 device.
16supported family codes:
17W1_THERM_DS18S20	0x10
18W1_THERM_DS1822		0x22
19W1_THERM_DS18B20	0x28
20W1_THERM_DS1825		0x3B
21W1_THERM_DS28EA00	0x42
22
23Support is provided through the sysfs w1_slave file.  Each open and
24read sequence will initiate a temperature conversion then provide two
25lines of ASCII output.  The first line contains the nine hex bytes
26read along with a calculated crc value and YES or NO if it matched.
27If the crc matched the returned values are retained.  The second line
28displays the retained values along with a temperature in millidegrees
29Centigrade after t=.
30
31Parasite powered devices are limited to one slave performing a
32temperature conversion at a time.  If none of the devices are parasite
33powered it would be possible to convert all the devices at the same
34time and then go back to read individual sensors.  That isn't
35currently supported.  The driver also doesn't support reduced
36precision (which would also reduce the conversion time).
37
38The module parameter strong_pullup can be set to 0 to disable the
39strong pullup, 1 to enable autodetection or 2 to force strong pullup.
40In case of autodetection, the driver will use the "READ POWER SUPPLY"
41command to check if there are pariste powered devices on the bus.
42If so, it will activate the master's strong pullup.
43In case the detection of parasite devices using this command fails
44(seems to be the case with some DS18S20) the strong pullup can
45be force-enabled.
46If the strong pullup is enabled, the master's strong pullup will be
47driven when the conversion is taking place, provided the master driver
48does support the strong pullup (or it falls back to a pullup
49resistor).  The DS18b20 temperature sensor specification lists a
50maximum current draw of 1.5mA and that a 5k pullup resistor is not
51sufficient.  The strong pullup is designed to provide the additional
52current required.
53
54The DS28EA00 provides an additional two pins for implementing a sequence
55detection algorithm.  This feature allows you to determine the physical
56location of the chip in the 1-wire bus without needing pre-existing
57knowledge of the bus ordering.  Support is provided through the sysfs
58w1_seq file.  The file will contain a single line with an integer value
59representing the device index in the bus starting at 0.
60