1 Kernel driver ds1621
2 ====================
3
4 Supported chips:
5
6 * Dallas Semiconductor / Maxim Integrated DS1621
7
8 Prefix: 'ds1621'
9
10 Addresses scanned: none
11
12 Datasheet: Publicly available from www.maximintegrated.com
13
14 * Dallas Semiconductor DS1625
15
16 Prefix: 'ds1625'
17
18 Addresses scanned: none
19
20 Datasheet: Publicly available from www.datasheetarchive.com
21
22 * Maxim Integrated DS1631
23
24 Prefix: 'ds1631'
25
26 Addresses scanned: none
27
28 Datasheet: Publicly available from www.maximintegrated.com
29
30 * Maxim Integrated DS1721
31
32 Prefix: 'ds1721'
33
34 Addresses scanned: none
35
36 Datasheet: Publicly available from www.maximintegrated.com
37
38 * Maxim Integrated DS1731
39
40 Prefix: 'ds1731'
41
42 Addresses scanned: none
43
44 Datasheet: Publicly available from www.maximintegrated.com
45
46 Authors:
47 - Christian W. Zuckschwerdt <zany@triq.net>
48 - valuable contributions by Jan M. Sendler <sendler@sendler.de>
49 - ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
50 with the help of Jean Delvare <jdelvare@suse.de>
51
52 Module Parameters
53 ------------------
54
55 * polarity int
56 Output's polarity:
57
58 * 0 = active high,
59 * 1 = active low
60
61 Description
62 -----------
63
64 The DS1621 is a (one instance) digital thermometer and thermostat. It has
65 both high and low temperature limits which can be user defined (i.e.
66 programmed into non-volatile on-chip registers). Temperature range is -55
67 degree Celsius to +125 in 0.5 increments. You may convert this into a
68 Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
69 parameter is not provided, original value is used.
70
71 As for the thermostat, behavior can also be programmed using the polarity
72 toggle. On the one hand ("heater"), the thermostat output of the chip,
73 Tout, will trigger when the low limit temperature is met or underrun and
74 stays high until the high limit is met or exceeded. On the other hand
75 ("cooler"), vice versa. That way "heater" equals "active low", whereas
76 "conditioner" equals "active high". Please note that the DS1621 data sheet
77 is somewhat misleading in this point since setting the polarity bit does
78 not simply invert Tout.
79
80 A second thing is that, during extensive testing, Tout showed a tolerance
81 of up to +/- 0.5 degrees even when compared against precise temperature
82 readings. Be sure to have a high vs. low temperature limit gap of al least
83 1.0 degree Celsius to avoid Tout "bouncing", though!
84
85 The alarm bits are set when the high or low limits are met or exceeded and
86 are reset by the module as soon as the respective temperature ranges are
87 left.
88
89 The alarm registers are in no way suitable to find out about the actual
90 status of Tout. They will only tell you about its history, whether or not
91 any of the limits have ever been met or exceeded since last power-up or
92 reset. Be aware: When testing, it showed that the status of Tout can change
93 with neither of the alarms set.
94
95 Since there is no version or vendor identification register, there is
96 no unique identification for these devices. Therefore, explicit device
97 instantiation is required for correct device identification and functionality
98 (one device per address in this address range: 0x48..0x4f).
99
100 The DS1625 is pin compatible and functionally equivalent with the DS1621,
101 but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are
102 also pin compatible with the DS1621 and provide multi-resolution support.
103
104 Additionally, the DS1721 data sheet says the temperature flags (THF and TLF)
105 are used internally, however, these flags do get set and cleared as the actual
106 temperature crosses the min or max settings (which by default are set to 75
107 and 80 degrees respectively).
108
109 Temperature Conversion
110 ----------------------
111
112 - DS1621 - 750ms (older devices may take up to 1000ms)
113 - DS1625 - 500ms
114 - DS1631 - 93ms..750ms for 9..12 bits resolution, respectively.
115 - DS1721 - 93ms..750ms for 9..12 bits resolution, respectively.
116 - DS1731 - 93ms..750ms for 9..12 bits resolution, respectively.
117
118 Note:
119 On the DS1621, internal access to non-volatile registers may last for 10ms
120 or less (unverified on the other devices).
121
122 Temperature Accuracy
123 --------------------
124
125 - DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees)
126 - DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees)
127 - DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees)
128 - DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees)
129 - DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees)
130
131 .. Note::
132
133 Please refer to the device datasheets for accuracy at other temperatures.
134
135 Temperature Resolution:
136 -----------------------
137 As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution
138 support, which is achieved via the R0 and R1 config register bits, where:
139
140 R0..R1
141 ------
142
143 == == ===============================
144 R0 R1
145 == == ===============================
146 0 0 9 bits, 0.5 degrees Celsius
147 1 0 10 bits, 0.25 degrees Celsius
148 0 1 11 bits, 0.125 degrees Celsius
149 1 1 12 bits, 0.0625 degrees Celsius
150 == == ===============================
151
152 .. Note::
153
154 At initial device power-on, the default resolution is set to 12-bits.
155
156 The resolution mode for the DS1631, DS1721, or DS1731 can be changed from
157 userspace, via the device 'update_interval' sysfs attribute. This attribute
158 will normalize the range of input values to the device maximum resolution
159 values defined in the datasheet as follows:
160
161 ============= ================== ===============
162 Resolution Conversion Time Input Range
163 (C/LSB) (msec) (msec)
164 ============= ================== ===============
165 0.5 93.75 0....94
166 0.25 187.5 95...187
167 0.125 375 188..375
168 0.0625 750 376..infinity
169 ============= ================== ===============
170
171 The following examples show how the 'update_interval' attribute can be
172 used to change the conversion time::
173
174 $ cat update_interval
175 750
176 $ cat temp1_input
177 22062
178 $
179 $ echo 300 > update_interval
180 $ cat update_interval
181 375
182 $ cat temp1_input
183 22125
184 $
185 $ echo 150 > update_interval
186 $ cat update_interval
187 188
188 $ cat temp1_input
189 22250
190 $
191 $ echo 1 > update_interval
192 $ cat update_interval
193 94
194 $ cat temp1_input
195 22000
196 $
197 $ echo 1000 > update_interval
198 $ cat update_interval
199 750
200 $ cat temp1_input
201 22062
202 $
203
204 As shown, the ds1621 driver automatically adjusts the 'update_interval'
205 user input, via a step function. Reading back the 'update_interval' value
206 after a write operation provides the conversion time used by the device.
207
208 Mathematically, the resolution can be derived from the conversion time
209 via the following function:
210
211 g(x) = 0.5 * [minimum_conversion_time/x]
212
213 where:
214
215 - 'x' = the output from 'update_interval'
216 - 'g(x)' = the resolution in degrees C per LSB.
217 - 93.75ms = minimum conversion time
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