diff options
| author | David Fries <david@fries.net> | 2008-10-15 22:04:43 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-10-16 11:21:49 -0700 |
| commit | 6cd159744eaf212f3729d154f3881230a7c19eb2 (patch) | |
| tree | c2a76ecf90e0b156f480044f26d6379dba46d7eb /Documentation/w1/slaves/w1_therm | |
| parent | 6a158c0de791a81eb761ccf26ead1bd0834abac2 (diff) | |
| download | blackbird-op-linux-6cd159744eaf212f3729d154f3881230a7c19eb2.tar.gz blackbird-op-linux-6cd159744eaf212f3729d154f3881230a7c19eb2.zip | |
W1: feature, w1_therm.c use strong pullup and documentation
Added strong pullup to thermal sensor driver and general documentation on
the sensor.
Signed-off-by: David Fries <david@fries.net>
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/w1/slaves/w1_therm')
| -rw-r--r-- | Documentation/w1/slaves/w1_therm | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/w1/slaves/w1_therm b/Documentation/w1/slaves/w1_therm new file mode 100644 index 000000000000..0403aaaba878 --- /dev/null +++ b/Documentation/w1/slaves/w1_therm @@ -0,0 +1,41 @@ +Kernel driver w1_therm +==================== + +Supported chips: + * Maxim ds18*20 based temperature sensors. + +Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru> + + +Description +----------- + +w1_therm provides basic temperature conversion for ds18*20 devices. +supported family codes: +W1_THERM_DS18S20 0x10 +W1_THERM_DS1822 0x22 +W1_THERM_DS18B20 0x28 + +Support is provided through the sysfs w1_slave file. Each open and +read sequence will initiate a temperature conversion then provide two +lines of ASCII output. The first line contains the nine hex bytes +read along with a calculated crc value and YES or NO if it matched. +If the crc matched the returned values are retained. The second line +displays the retained values along with a temperature in millidegrees +Centigrade after t=. + +Parasite powered devices are limited to one slave performing a +temperature conversion at a time. If none of the devices are parasite +powered it would be possible to convert all the devices at the same +time and then go back to read individual sensors. That isn't +currently supported. The driver also doesn't support reduced +precision (which would also reduce the conversion time). + +The module parameter strong_pullup can be set to 0 to disable the +strong pullup or 1 to enable. If enabled the 5V strong pullup will be +enabled when the conversion is taking place provided the master driver +must support the strong pullup (or it falls back to a pullup +resistor). The DS18b20 temperature sensor specification lists a +maximum current draw of 1.5mA and that a 5k pullup resistor is not +sufficient. The strong pullup is designed to provide the additional +current required. |
