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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 | |
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. |
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. |
64 |
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