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