1DS18B20(3) One-Wire File System DS18B20(3)
2
3
4
6 DS18B20
7 - Programmable Resolution 1-Wire Digital Thermometer
8
9 MAX31820
10 - Ambient Temperature Sensor
11
13 Thermometer.
14
15 28 [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9 | tem‐
16 perature10 | temperature11 | temperature12 | latesttemp | die | power |
17 temphigh | templow | tempres | errata/die | errata/trim | errata/trim‐
18 blanket | errata/trimvalid | address | crc8 | id | locator | r_address
19 | r_id | r_locator | type ]]
20
22 28
23
25 power
26 read-only,yes-no
27 Is the chip powered externally (=1) or from the parasitically from the
28 data bus (=0)?
29
30 temperature
31 read-only, floating point
32 Measured temperature with 12 bit resolution.
33
34 temperature9 temperature10 temperature11 temperature12
35 read-only, floating point
36 Measured temperature at 9 to 12 bit resolution. There is a tradeoff of
37 time versus accuracy in the temperature measurement.
38
39 latesttemp
40 read-only, floating point
41 Measured temperature at 9 to 12 bit resolution, depending on the reso‐
42 lution of the latest conversion on this chip. Reading this node will
43 never trigger a temperature conversion. Intended for use in conjunction
44 with /simultaneous/temperature.
45
46 fasttemp
47 read-only, floating point
48 Equivalent to temperature9
49
51 When the device exceeds either temphigh or templow temperature thresh‐
52 old the device is in the alarm state, and will appear in the alarm
53 directory. This provides an easy way to poll for temperatures that are
54 unsafe, especially if simultaneous temperature conversion is done.
55
56 Units for the temperature alarms are in the same temperature scale that
57 was set for temperature measurements.
58
59 Temperature thresholds are stored in non-volatile memory and persist
60 until changed, even if power is lost.
61
62 temphigh
63 read-write, integer
64 Shows or sets the lower limit for the high temperature alarm state.
65
66 templow
67 read-write, integer
68 Shows or sets the upper limit for the low temperature alarm state.
69
71 tempres
72 read-write, integer
73 The device employs a non-volatile memory to store the default tempera‐
74 ture resolution (9, 10, 11 or 12 bits) to be applied after power-up.
75 This is useful if you use simultaneous temperature conversions. Reading
76 this node gives you the value stored in the non-volatile memory. Writ‐
77 ing sets a new power-on resolution value.
78
79 As a side effect, reading this node resets the temperature resolution
80 used by simultaneous temperature conversions to its power-on value. It
81 also affects the resolution value used by latesttemp, to scale the lat‐
82 est conversion value, so make sure to re-sample the temperature before
83 accessing latesttemp after writing or reading the tempres value.
84
86 There are a group of obscure internal properties exposed to protect
87 against an hardware defect in certain batches of the B7 die of some
88 DS18x20 chips. See http://www.1wire.org/en-us/pg_18.html or request
89 AN247.pdf from Dallas directly.
90
91 errata/die
92 read-only,ascii
93 Two character manufacturing die lot. "B6" "B7" or "C2"
94
95 errata/trim
96 read-write,unsigned integer
97 32 bit trim value in the EEPROM of the chip. When written, it does not
98 seem to read back. Used for a production problem in the B7 die.
99
100 Read allowed for all chips. Only the B7 chips can be written.
101
102 errata/trimblanket
103 read-write,yes-no
104 Writing non-zero (=1) puts a default trim value in the chip. Only
105 applied to the B7 die. Reading will be true (non-zero) if trim value
106 is the blanket value. Again, only B7 chips will register true, and
107 since the written trim values cannot be read, this value may have lit‐
108 tle utility.
109
110 errata/trimvalid
111 read-only,yes-no
112 Is the trim value in the valid range? Non-zero if true, which includes
113 all non-B7 chips.
114
116 address
117 r_address
118 read-only, ascii
119 The entire 64-bit unique ID. Given as upper case hexidecimal digits
120 (0-9A-F).
121 address starts with the family code
122 r address is the address in reverse order, which is often used in other
123 applications and labeling.
124
125 crc8
126 read-only, ascii
127 The 8-bit error correction portion. Uses cyclic redundancy check. Com‐
128 puted from the preceding 56 bits of the unique ID number. Given as
129 upper case hexidecimal digits (0-9A-F).
130
131 family
132 read-only, ascii
133 The 8-bit family code. Unique to each type of device. Given as upper
134 case hexidecimal digits (0-9A-F).
135
136 id
137 r_id
138 read-only, ascii
139 The 48-bit middle portion of the unique ID number. Does not include the
140 family code or CRC. Given as upper case hexidecimal digits (0-9A-F).
141 r id is the id in reverse order, which is often used in other applica‐
142 tions and labeling.
143
144 locator
145 r_locator
146 read-only, ascii
147 Uses an extension of the 1-wire design from iButtonLink company that
148 associated 1-wire physical connections with a unique 1-wire code. If
149 the connection is behind a Link Locator the locator will show a unique
150 8-byte number (16 character hexidecimal) starting with family code FE.
151 If no Link Locator is between the device and the master, the locator
152 field will be all FF.
153 r locator is the locator in reverse order.
154
155 present (DEPRECATED)
156 read-only, yes-no
157 Is the device currently present on the 1-wire bus?
158
159 type
160 read-only, ascii
161 Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging
162 (iButton vs chip) will not be distiguished.
163
165 1-Wire
166 1-wire is a wiring protocol and series of devices designed and manufac‐
167 tured by Dallas Semiconductor, Inc. The bus is a low-power low-speed
168 low-connector scheme where the data line can also provide power.
169
170 Each device is uniquely and unalterably numbered during manufacture.
171 There are a wide variety of devices, including memory, sensors (humid‐
172 ity, temperature, voltage, contact, current), switches, timers and data
173 loggers. More complex devices (like thermocouple sensors) can be built
174 with these basic devices. There are also 1-wire devices that have
175 encryption included.
176
177 The 1-wire scheme uses a single bus master and multiple slaves on the
178 same wire. The bus master initiates all communication. The slaves can
179 be individually discovered and addressed using their unique ID.
180
181 Bus masters come in a variety of configurations including serial, par‐
182 allel, i2c, network or USB adapters.
183
184 OWFS design
185 OWFS is a suite of programs that designed to make the 1-wire bus and
186 its devices easily accessible. The underlying principle is to create a
187 virtual filesystem, with the unique ID being the directory, and the
188 individual properties of the device are represented as simple files
189 that can be read and written.
190
191 Details of the individual slave or master design are hidden behind a
192 consistent interface. The goal is to provide an easy set of tools for a
193 software designer to create monitoring or control applications. There
194 are some performance enhancements in the implementation, including data
195 caching, parallel access to bus masters, and aggregation of device com‐
196 munication. Still the fundemental goal has been ease of use, flexibil‐
197 ity and correctness rather than speed.
198
199 DS18B20
200 The DS18B20 (3) is one of several available 1-wire temperature sensors.
201 It is the replacement for the DS18S20 (3) Alternatives are DS1822 (3)
202 as well as temperature/voltage measurements in the DS2436 (3) and
203 DS2438 (3). For truly versatile temperature measurements, see the pro‐
204 tean DS1921 (3) Thermachron (3).
205
206 The MAX31820 is functionally identical to the DS18B20 except for it's
207 voltage requirements.
208 The DS18B20 (3) can select between 4 resolutions. In general, high res‐
209 olution is the best choice unless your application is truly time-con‐
210 strained.
211
213 All 1-wire devices are factory assigned a unique 64-bit address. This
214 address is of the form:
215
216 Family Code
217 8 bits
218
219 Address
220 48 bits
221
222 CRC 8 bits
223
224 Addressing under OWFS is in hexidecimal, of form:
225
226 01.123456789ABC
227
228 where 01 is an example 8-bit family code, and 12345678ABC is an example
229 48 bit address.
230
231 The dot is optional, and the CRC code can included. If included, it
232 must be correct.
233
235 http://pdfserv.maxim-ic.com/en/ds/DS18B20.pdf
236
238 Programs
239 owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1)
240 owwrite (1) owpresent (1) owtap (1)
241
242 Configuration and testing
243 owfs (5) owtap (1) owmon (1)
244
245 Language bindings
246 owtcl (3) owperl (3) owcapi (3)
247
248 Clocks
249 DS1427 (3) DS1904 (3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3)
250 DS2417 (3)
251
252 ID
253 DS2401 (3) DS2411 (3) DS1990A (3)
254
255 Memory
256 DS1982 (3) DS1985 (3) DS1986 (3) DS1991 (3) DS1992 (3) DS1993 (3)
257 DS1995 (3) DS1996 (3) DS2430A (3) DS2431 (3) DS2433 (3) DS2502 (3)
258 DS2506 (3) DS28E04 (3) DS28EC20 (3)
259
260 Switches
261 DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)
262
263 Temperature
264 DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3)
265 DS1921 (3) DS1821 (3) DS28EA00 (3) DS28E04 (3) EDS0064 (3) EDS0065 (3)
266 EDS0066 (3) EDS0067 (3) EDS0068 (3) EDS0071 (3) EDS0072 (3) MAX31826
267 [1m(3)
268
269 Humidity
270 DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)
271
272 Voltage
273 DS2450 (3)
274
275 Resistance
276 DS2890 (3)
277
278 Multifunction (current, voltage, temperature)
279 DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3)
280 DS2760 (3) DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)
281
282 Counter
283 DS2423 (3)
284
285 LCD Screen
286 LCD (3) DS2408 (3)
287
288 Crypto
289 DS1977 (3)
290
291 Pressure
292 DS2406 (3) TAI8570 (3) EDS0066 (3) EDS0068 (3)
293
294 Moisture
295 EEEF (3) DS2438 (3)
296
298 http://www.owfs.org
299
301 Paul Alfille (paul.alfille@gmail.com)
302
303
304
305OWFS Manpage 2003 DS18B20(3)