| R.Marek@sh.cvut.cz | 7f15b66 | 2005-05-26 12:42:19 +0000 | [diff] [blame] | 1 | Kernel driver ds1621 |
| 2 | ==================== |
| 3 | |
| 4 | Supported 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 | |
| 16 | Authors: |
| 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 | |
| 22 | Module Parameters |
| 23 | ------------------ |
| 24 | |
| 25 | * polarity int |
| 26 | Output's polarity: 0 = active high, 1 = active low |
| 27 | |
| 28 | Description |
| 29 | ----------- |
| 30 | |
| 31 | The DS1621 is a (one instance) digital thermometer and thermostat. It has |
| 32 | both high and low temperature limits which can be user defined (i.e. |
| 33 | programmed into non-volatile on-chip registers). Temperature range is -55 |
| 34 | degree Celsius to +125 in 0.5 increments. You may convert this into a |
| 35 | Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity |
| 36 | parameter is not provided, original value is used. |
| 37 | |
| 38 | As for the thermostat, behavior can also be programmed using the polarity |
| 39 | toggle. On the one hand ("heater"), the thermostat output of the chip, |
| 40 | Tout, will trigger when the low limit temperature is met or underrun and |
| 41 | stays 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 |
| 44 | is somewhat misleading in this point since setting the polarity bit does |
| 45 | not simply invert Tout. |
| 46 | |
| 47 | A second thing is that, during extensive testing, Tout showed a tolerance |
| 48 | of up to +/- 0.5 degrees even when compared against precise temperature |
| 49 | readings. Be sure to have a high vs. low temperature limit gap of al least |
| 50 | 1.0 degree Celsius to avoid Tout "bouncing", though! |
| 51 | |
| Jean Delvare | 25f3311 | 2009-03-30 21:46:41 +0200 | [diff] [blame^] | 52 | The alarm bits are set when the high or low limits are met or exceeded and |
| 53 | are reset by the module as soon as the respective temperature ranges are |
| 54 | left. |
| R.Marek@sh.cvut.cz | 7f15b66 | 2005-05-26 12:42:19 +0000 | [diff] [blame] | 55 | |
| 56 | The alarm registers are in no way suitable to find out about the actual |
| 57 | status of Tout. They will only tell you about its history, whether or not |
| 58 | any of the limits have ever been met or exceeded since last power-up or |
| 59 | reset. Be aware: When testing, it showed that the status of Tout can change |
| 60 | with neither of the alarms set. |
| 61 | |
| 62 | Temperature conversion of the DS1621 takes up to 1000ms; internal access to |
| 63 | non-volatile registers may last for 10ms or below. |