DS1822(3)

1DS1822(3)                    One-Wire File System                    DS1822(3)
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NAME

6       DS1822 - Econo 1-Wire Digital Thermometer
7

SYNOPSIS

9       Thermometer.
10
11       22  [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9 | tem‐
12       perature10 | temperature11 | temperature12 | latesttemp | die | power |
13       temphigh | templow | tempres | trim | trimblanket | trimvalid | address
14       | crc8 | id | locator | r_address | r_id | r_locator | type ]]
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FAMILY CODE

17       22
18

SPECIAL PROPERTIES

20   power
21       read-only,yes-no
22       Is the chip powered externally (=1) or from the parasitically from  the
23       data bus (=0)?
24
25   temperature
26       read-only, floating point
27       Measured temperature with 12 bit resolution.
28
29   temperature9 temperature10 temperature11 temperature12
30       read-only, floating point
31       Measured  temperature at 9 to 12 bit resolution. There is a tradeoff of
32       time versus accuracy in the temperature measurement.
33
34   latesttemp
35       read-only, floating point
36       Measured temperature at 9 to 12 bit resolution, depending on the  reso‐
37       lution  of  the  latest conversion on this chip. Reading this node will
38       never trigger a temperature conversion. Intended for use in conjunction
39       with /simultaneous/temperature.
40
41   fasttemp
42       read-only, floating point
43       Equivalent to temperature9
44

TEMPERATURE ALARM LIMITS

46       When  the device exceeds either temphigh or templow temperature thresh‐
47       old the device is in the alarm state, and  will  appear  in  the  alarm
48       directory.  This provides an easy way to poll for temperatures that are
49       unsafe, especially if simultaneous temperature conversion is done.
50
51       Units for the temperature alarms are in the same temperature scale that
52       was set for temperature measurements.
53
54       Temperature  thresholds  are  stored in non-volatile memory and persist
55       until changed, even if power is lost.
56
57   temphigh
58       read-write, integer
59       Shows or sets the lower limit for the high temperature alarm state.
60
61   templow
62       read-write, integer
63       Shows or sets the upper limit for the low temperature alarm state.
64

TEMPERATURE RESOLUTION DEFAULT VALUE

66   tempres
67       read-write, integer
68       The device employs a non-volatile memory to store the default  tempera‐
69       ture  resolution  (9,  10, 11 or 12 bits) to be applied after power-up.
70       This is useful if you use simultaneous temperature conversions. Reading
71       this  node gives you the value stored in the non-volatile memory. Writ‐
72       ing sets a new power-on resolution value.
73
74       As a side effect, reading this node resets the  temperature  resolution
75       used  by simultaneous temperature conversions to its power-on value. It
76       also affects the resolution value used by latesttemp, to scale the lat‐
77       est  conversion value, so make sure to re-sample the temperature before
78       accessing latesttemp after writing or reading the tempres value.
79

TEMPERATURE ERRATA

81       There are a group of obscure internal  properties  exposed  to  protect
82       against  an  hardware  defect  in certain batches of the B7 die of some
83       DS18x20 chips.  See  http://www.1wire.org/en-us/pg_18.html  or  request
84       AN247.pdf from Dallas directly.
85
86   errata/die
87       read-only,ascii
88       Two character manufacturing die lot. "B6" "B7" or "C2"
89
90   errata/trim
91       read-write,unsigned integer
92       32  bit trim value in the EEPROM of the chip. When written, it does not
93       seem to read back. Used for a production problem in the B7 die.
94
95       Read allowed for all chips. Only the B7 chips can be written.
96
97   errata/trimblanket
98       read-write,yes-no
99       Writing non-zero (=1) puts a default  trim  value  in  the  chip.  Only
100       applied  to  the B7 die.  Reading will be true (non-zero) if trim value
101       is the blanket value. Again, only B7  chips  will  register  true,  and
102       since  the written trim values cannot be read, this value may have lit‐
103       tle utility.
104
105   errata/trimvalid
106       read-only,yes-no
107       Is the trim value in the valid range? Non-zero if true, which  includes
108       all non-B7 chips.
109

STANDARD PROPERTIES

111   address
112   r_address
113       read-only, ascii
114       The  entire  64-bit  unique  ID. Given as upper case hexidecimal digits
115       (0-9A-F).
116       address starts with the family code
117       r address is the address in reverse order, which is often used in other
118       applications and labeling.
119
120   crc8
121       read-only, ascii
122       The  8-bit error correction portion. Uses cyclic redundancy check. Com‐
123       puted from the preceding 56 bits of the  unique  ID  number.  Given  as
124       upper case hexadecimal digits (0-9A-F).
125
126   family
127       read-only, ascii
128       The  8-bit  family  code. Unique to each type of device. Given as upper
129       case hexadecimal digits (0-9A-F).
130
131   id
132   r_id
133       read-only, ascii
134       The 48-bit middle portion of the unique ID number. Does not include the
135       family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
136       r  id is the id in reverse order, which is often used in other applica‐
137       tions and labeling.
138
139   locator
140   r_locator
141       read-only, ascii
142       Uses an extension of the 1-wire design from  iButtonLink  company  that
143       associated  1-wire  physical  connections with a unique 1-wire code. If
144       the connection is behind a Link Locator the locator will show a  unique
145       8-byte number (16 character hexadecimal) starting with family code FE.
146       If  no  Link  Locator is between the device and the master, the locator
147       field will be all FF.
148       r locator is the locator in reverse order.
149
150   present (DEPRECATED)
151       read-only, yes-no
152       Is the device currently present on the 1-wire bus?
153
154   type
155       read-only, ascii
156       Part name assigned by Dallas Semi. E.g.  DS2401  Alternative  packaging
157       (iButton vs chip) will not be distiguished.
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DESCRIPTION

160   1-Wire
161       1-wire is a wiring protocol and series of devices designed and manufac‐
162       tured by Dallas Semiconductor, Inc. The bus is  a  low-power  low-speed
163       low-connector scheme where the data line can also provide power.
164
165       Each  device  is  uniquely and unalterably numbered during manufacture.
166       There are a wide variety of devices, including memory, sensors  (humid‐
167       ity, temperature, voltage, contact, current), switches, timers and data
168       loggers. More complex devices (like thermocouple sensors) can be  built
169       with  these  basic  devices.  There  are  also 1-wire devices that have
170       encryption included.
171
172       The 1-wire scheme uses a single bus master and multiple slaves  on  the
173       same  wire.  The bus master initiates all communication. The slaves can
174       be individually discovered and addressed using their unique ID.
175
176       Bus masters come in a variety of configurations including serial,  par‐
177       allel, i2c, network or USB adapters.
178
179   OWFS design
180       OWFS  is  a  suite of programs that designed to make the 1-wire bus and
181       its devices easily accessible. The underlying principle is to create  a
182       virtual  filesystem,  with  the  unique ID being the directory, and the
183       individual properties of the device are  represented  as  simple  files
184       that can be read and written.
185
186       Details  of  the  individual slave or master design are hidden behind a
187       consistent interface. The goal is to provide an easy set of tools for a
188       software  designer  to create monitoring or control applications. There
189       are some performance enhancements in the implementation, including data
190       caching, parallel access to bus masters, and aggregation of device com‐
191       munication. Still the fundamental goal has been ease of use,  flexibil‐
192       ity and correctness rather than speed.
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194   DS1822
195       The  DS1822 (3) is one of several available 1-wire temperature sensors.
196       Alternatives are the DS18S20 (3),  DS18B20  (3)  as  well  as  tempera‐
197       ture/voltage  measurements in the DS2436 (3) and DS2438 (3).  For truly
198       versatile temperature measurements, see the protean DS1921 (3)  Therma‐
199       chron (3).
200
201       Although  the DS1822 (3) can select between 4 resolutions, this program
202       simplifies the interface by only implementing the fastest/roughest  and
203       slowest/best.
204

ADDRESSING

206       All  1-wire  devices are factory assigned a unique 64-bit address. This
207       address is of the form:
208
209       Family Code
210              8 bits
211
212       Address
213              48 bits
214
215       CRC    8 bits
216
217       Addressing under OWFS is in hexadecimal, of form:
218
219              01.123456789ABC
220
221       where 01 is an example 8-bit family code, and 12345678ABC is an example
222       48 bit address.
223
224       The  dot  is  optional,  and the CRC code can included. If included, it
225       must be correct.
226

DATASHEET

228       http://pdfserv.maxim-ic.com/en/ds/DS1822.pdf
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AVAILABILITY

291       http://www.owfs.org
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AUTHOR

294       Paul Alfille (paul.alfille@gmail.com)
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298OWFS Manpage                         2003                            DS1822(3)