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.
15supported family codes:
16W1_THERM_DS18S20	0x10
17W1_THERM_DS1822		0x22
18W1_THERM_DS18B20	0x28
19W1_THERM_DS1825		0x3B
20
21Support is provided through the sysfs w1_slave file.  Each open and
22read sequence will initiate a temperature conversion then provide two
23lines of ASCII output.  The first line contains the nine hex bytes
24read along with a calculated crc value and YES or NO if it matched.
25If the crc matched the returned values are retained.  The second line
26displays the retained values along with a temperature in millidegrees
27Centigrade after t=.
28
29Parasite powered devices are limited to one slave performing a
30temperature conversion at a time.  If none of the devices are parasite
31powered it would be possible to convert all the devices at the same
32time and then go back to read individual sensors.  That isn't
33currently supported.  The driver also doesn't support reduced
34precision (which would also reduce the conversion time).
35
36The module parameter strong_pullup can be set to 0 to disable the
37strong pullup, 1 to enable autodetection or 2 to force strong pullup.
38In case of autodetection, the driver will use the "READ POWER SUPPLY"
39command to check if there are pariste powered devices on the bus.
40If so, it will activate the master's strong pullup.
41In case the detection of parasite devices using this command fails
42(seems to be the case with some DS18S20) the strong pullup can
43be force-enabled.
44If the strong pullup is enabled, the master's strong pullup will be
45driven when the conversion is taking place, provided the master driver
46does support the strong pullup (or it falls back to a pullup
47resistor).  The DS18b20 temperature sensor specification lists a
48maximum current draw of 1.5mA and that a 5k pullup resistor is not
49sufficient.  The strong pullup is designed to provide the additional
50current required.
51