From 6cd159744eaf212f3729d154f3881230a7c19eb2 Mon Sep 17 00:00:00 2001 From: David Fries Date: Wed, 15 Oct 2008 22:04:43 -0700 Subject: 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 Signed-off-by: Evgeniy Polyakov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/w1/00-INDEX | 2 ++ Documentation/w1/slaves/00-INDEX | 4 ++++ Documentation/w1/slaves/w1_therm | 41 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 47 insertions(+) create mode 100644 Documentation/w1/slaves/00-INDEX create mode 100644 Documentation/w1/slaves/w1_therm (limited to 'Documentation') diff --git a/Documentation/w1/00-INDEX b/Documentation/w1/00-INDEX index 5270cf4cb10..cb49802745d 100644 --- a/Documentation/w1/00-INDEX +++ b/Documentation/w1/00-INDEX @@ -1,5 +1,7 @@ 00-INDEX - This file +slaves/ + - Drivers that provide support for specific family codes. masters/ - Individual chips providing 1-wire busses. w1.generic diff --git a/Documentation/w1/slaves/00-INDEX b/Documentation/w1/slaves/00-INDEX new file mode 100644 index 00000000000..f8101d6b07b --- /dev/null +++ b/Documentation/w1/slaves/00-INDEX @@ -0,0 +1,4 @@ +00-INDEX + - This file +w1_therm + - The Maxim/Dallas Semiconductor ds18*20 temperature sensor. diff --git a/Documentation/w1/slaves/w1_therm b/Documentation/w1/slaves/w1_therm new file mode 100644 index 00000000000..0403aaaba87 --- /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 + + +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. -- cgit v1.2.3-70-g09d2