64 lines
2.6 KiB
Plaintext
64 lines
2.6 KiB
Plaintext
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Kernel driver ds1621
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====================
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Supported chips:
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* Dallas Semiconductor DS1621
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Prefix: 'ds1621'
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Addresses scanned: I2C 0x48 - 0x4f
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Datasheet: Publicly available at the Dallas Semiconductor website
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http://www.dalsemi.com/
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* Dallas Semiconductor DS1625
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Prefix: 'ds1621'
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Addresses scanned: I2C 0x48 - 0x4f
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Datasheet: Publicly available at the Dallas Semiconductor website
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http://www.dalsemi.com/
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Authors:
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Christian W. Zuckschwerdt <zany@triq.net>
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valuable contributions by Jan M. Sendler <sendler@sendler.de>
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ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
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with the help of Jean Delvare <khali@linux-fr.org>
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Module Parameters
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------------------
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* polarity int
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Output's polarity: 0 = active high, 1 = active low
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Description
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-----------
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The DS1621 is a (one instance) digital thermometer and thermostat. It has
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both high and low temperature limits which can be user defined (i.e.
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programmed into non-volatile on-chip registers). Temperature range is -55
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degree Celsius to +125 in 0.5 increments. You may convert this into a
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Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
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parameter is not provided, original value is used.
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As for the thermostat, behavior can also be programmed using the polarity
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toggle. On the one hand ("heater"), the thermostat output of the chip,
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Tout, will trigger when the low limit temperature is met or underrun and
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stays high until the high limit is met or exceeded. On the other hand
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("cooler"), vice versa. That way "heater" equals "active low", whereas
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"conditioner" equals "active high". Please note that the DS1621 data sheet
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is somewhat misleading in this point since setting the polarity bit does
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not simply invert Tout.
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A second thing is that, during extensive testing, Tout showed a tolerance
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of up to +/- 0.5 degrees even when compared against precise temperature
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readings. Be sure to have a high vs. low temperature limit gap of al least
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1.0 degree Celsius to avoid Tout "bouncing", though!
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The alarm bits are set when the high or low limits are met or exceeded and
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are reset by the module as soon as the respective temperature ranges are
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left.
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The alarm registers are in no way suitable to find out about the actual
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status of Tout. They will only tell you about its history, whether or not
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any of the limits have ever been met or exceeded since last power-up or
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reset. Be aware: When testing, it showed that the status of Tout can change
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with neither of the alarms set.
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Temperature conversion of the DS1621 takes up to 1000ms; internal access to
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non-volatile registers may last for 10ms or below.
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