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- Kernel driver w1_therm
- ====================
- Supported chips:
- * Maxim ds18*20 based temperature sensors.
- * Maxim ds1825 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
- W1_THERM_DS1825 0x3B
- 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.
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