42 lines
1.6 KiB
Text
42 lines
1.6 KiB
Text
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Kernel driver w1_therm
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====================
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Supported chips:
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* Maxim ds18*20 based temperature sensors.
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Author: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
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Description
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-----------
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w1_therm provides basic temperature conversion for ds18*20 devices.
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supported family codes:
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W1_THERM_DS18S20 0x10
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W1_THERM_DS1822 0x22
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W1_THERM_DS18B20 0x28
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Support is provided through the sysfs w1_slave file. Each open and
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read sequence will initiate a temperature conversion then provide two
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lines of ASCII output. The first line contains the nine hex bytes
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read along with a calculated crc value and YES or NO if it matched.
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If the crc matched the returned values are retained. The second line
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displays the retained values along with a temperature in millidegrees
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Centigrade after t=.
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Parasite powered devices are limited to one slave performing a
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temperature conversion at a time. If none of the devices are parasite
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powered it would be possible to convert all the devices at the same
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time and then go back to read individual sensors. That isn't
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currently supported. The driver also doesn't support reduced
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precision (which would also reduce the conversion time).
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The module parameter strong_pullup can be set to 0 to disable the
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strong pullup or 1 to enable. If enabled the 5V strong pullup will be
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enabled when the conversion is taking place provided the master driver
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must support the strong pullup (or it falls back to a pullup
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resistor). The DS18b20 temperature sensor specification lists a
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maximum current draw of 1.5mA and that a 5k pullup resistor is not
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sufficient. The strong pullup is designed to provide the additional
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current required.
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