Based on kernel version 3.19. Page generated on 2015-02-13 21:23 EST.
1 Kernel driver w1_therm 2 ==================== 3 4 Supported chips: 5 * Maxim ds18*20 based temperature sensors. 6 * Maxim ds1825 based temperature sensors. 7 8 Author: Evgeniy Polyakov <firstname.lastname@example.org> 9 10 11 Description 12 ----------- 13 14 w1_therm provides basic temperature conversion for ds18*20 devices. 15 supported family codes: 16 W1_THERM_DS18S20 0x10 17 W1_THERM_DS1822 0x22 18 W1_THERM_DS18B20 0x28 19 W1_THERM_DS1825 0x3B 20 21 Support is provided through the sysfs w1_slave file. Each open and 22 read sequence will initiate a temperature conversion then provide two 23 lines of ASCII output. The first line contains the nine hex bytes 24 read along with a calculated crc value and YES or NO if it matched. 25 If the crc matched the returned values are retained. The second line 26 displays the retained values along with a temperature in millidegrees 27 Centigrade after t=. 28 29 Parasite powered devices are limited to one slave performing a 30 temperature conversion at a time. If none of the devices are parasite 31 powered it would be possible to convert all the devices at the same 32 time and then go back to read individual sensors. That isn't 33 currently supported. The driver also doesn't support reduced 34 precision (which would also reduce the conversion time). 35 36 The module parameter strong_pullup can be set to 0 to disable the 37 strong pullup, 1 to enable autodetection or 2 to force strong pullup. 38 In case of autodetection, the driver will use the "READ POWER SUPPLY" 39 command to check if there are pariste powered devices on the bus. 40 If so, it will activate the master's strong pullup. 41 In case the detection of parasite devices using this command fails 42 (seems to be the case with some DS18S20) the strong pullup can 43 be force-enabled. 44 If the strong pullup is enabled, the master's strong pullup will be 45 driven when the conversion is taking place, provided the master driver 46 does support the strong pullup (or it falls back to a pullup 47 resistor). The DS18b20 temperature sensor specification lists a 48 maximum current draw of 1.5mA and that a 5k pullup resistor is not 49 sufficient. The strong pullup is designed to provide the additional 50 current required.