About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / hwmon / ds1621




Custom Search

Based on kernel version 3.15.4. Page generated on 2014-07-07 09:03 EST.

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

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.