w1/slaves/w1_therm.rst

16 -----------
18 w1_therm provides basic temperature conversion for ds18*20, ds28ea00, GX20MH01
32 read sequence will initiate a temperature conversion, then provide two
46 in the module), it will drive the line high during the longer conversion
48 ``therm_bulk_read`` will return 0 if no bulk conversion pending,
49 -1 if at least one sensor still in conversion, 1 if conversion is complete
52 may return empty if conversion is still in progress. Note that if a bulk
57 A strong pullup will be applied during the conversion if required.
59 ``conv_time`` is used to get current conversion time (read), and
60 adjust it (write). A temperature conversion time depends on the device type and
61 its current resolution. Default conversion time is set by the driver according
62 to the device datasheet. A conversion time for many original device clones
63 deviate from datasheet specs. There are three options: 1) manually set the
64 correct conversion time by writing a value in milliseconds to ``conv_time``; 2)
65 auto measure and set a conversion time by writing ``1`` to
66 ``conv_time``; 3) use ``features`` to enable poll for conversion
68 the default conversion time write ``0`` to ``conv_time``.
72 the sensor. Resolution is reset when the sensor gets power-cycled.
81 Some non-genuine DS18B20 chips are fixed in 12-bit mode only, so the actual
84 Note: Changing the resolution reverts the conversion time to default.
86 The write-only sysfs entry ``eeprom_cmd`` is an alternative for EEPROM operations.
94 Values shall be space separated and in the device range (typical -55 degC
106 be force-enabled.
109 driven when the conversion is taking place, provided the master driver
118 location of the chip in the 1-wire bus without needing pre-existing
124 Insufficient power in parasite mode, line noise and insufficient conversion
125 time may lead to conversion failure. Original DS18B20 and some clones allow for
126 detection of invalid conversion. Write bit mask ``1`` to ``features`` to enable
127 checking the conversion success. If byte 6 of scratchpad memory is 0xC after
128 conversion and temperature reads 85.00 (powerup value) or 127.94 (insufficient
129 power), the driver returns a conversion error. Bit mask ``2`` enables poll for
130 conversion completion (normal power only) by generating read cycles on the bus
131 after conversion starts. In parasite power mode this feature is not available.
133 Documentation/ABI/testing/sysfs-driver-w1_therm
136 compatible with DS18B20. Added are lowest 2\ :sup:`-5`, 2\ :sup:`-6` temperature
138 resolutions. The device is powered up in 14-bit resolution mode. The conversion
144 indicating 15, but the device is always operating in 14-bit resolution mode.