linux/Documentation/hwmon/ds1621
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   1Kernel driver ds1621
   2====================
   3
   4Supported chips:
   5  * Dallas Semiconductor DS1621
   6    Prefix: 'ds1621'
   7    Addresses scanned: I2C 0x48 - 0x4f
   8    Datasheet: Publicly available at the Dallas Semiconductor website
   9               http://www.dalsemi.com/
  10  * Dallas Semiconductor DS1625
  11    Prefix: 'ds1621'
  12    Addresses scanned: I2C 0x48 - 0x4f
  13    Datasheet: Publicly available at the Dallas Semiconductor website
  14               http://www.dalsemi.com/
  15
  16Authors:
  17        Christian W. Zuckschwerdt <zany@triq.net>
  18        valuable contributions by Jan M. Sendler <sendler@sendler.de>
  19        ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
  20        with the help of Jean Delvare <khali@linux-fr.org>
  21
  22Module Parameters
  23------------------
  24
  25* polarity int
  26  Output's polarity: 0 = active high, 1 = active low
  27
  28Description
  29-----------
  30
  31The DS1621 is a (one instance) digital thermometer and thermostat. It has
  32both high and low temperature limits which can be user defined (i.e.
  33programmed into non-volatile on-chip registers). Temperature range is -55
  34degree Celsius to +125 in 0.5 increments. You may convert this into a
  35Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
  36parameter is not provided, original value is used.
  37
  38As for the thermostat, behavior can also be programmed using the polarity
  39toggle. On the one hand ("heater"), the thermostat output of the chip,
  40Tout, will trigger when the low limit temperature is met or underrun and
  41stays high until the high limit is met or exceeded. On the other hand
  42("cooler"), vice versa. That way "heater" equals "active low", whereas
  43"conditioner" equals "active high". Please note that the DS1621 data sheet
  44is somewhat misleading in this point since setting the polarity bit does
  45not simply invert Tout.
  46
  47A second thing is that, during extensive testing, Tout showed a tolerance
  48of up to +/- 0.5 degrees even when compared against precise temperature
  49readings. Be sure to have a high vs. low temperature limit gap of al least
  501.0 degree Celsius to avoid Tout "bouncing", though!
  51
  52The alarm bits are set when the high or low limits are met or exceeded and
  53are reset by the module as soon as the respective temperature ranges are
  54left.
  55
  56The alarm registers are in no way suitable to find out about the actual
  57status of Tout. They will only tell you about its history, whether or not
  58any of the limits have ever been met or exceeded since last power-up or
  59reset. Be aware: When testing, it showed that the status of Tout can change
  60with neither of the alarms set.
  61
  62Temperature conversion of the DS1621 takes up to 1000ms; internal access to
  63non-volatile registers may last for 10ms or below.
  64
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