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7f15b664 RM |
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 | ||
25f3311a JD |
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. | |
7f15b664 RM |
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. |