DS18S20(3)

1DS18S20(3)                   One-Wire File System                   DS18S20(3)
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NAME

6       DS18S20
7              - High-Precision 1-Wire Digital Thermometer
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9       DS1920 - iButton version of the thermometer
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SYNOPSIS

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

20       10
21

SPECIAL PROPERTIES

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

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

69       There are a group of obscure internal  properties  exposed  to  protect
70       against  an  hardware  defect  in certain batches of the B7 die of some
71       DS18x20 chips.  See  http://www.1wire.org/en-us/pg_18.html  or  request
72       AN247.pdf from Dallas directly.
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74   errata/die
75       read-only,ascii
76       Two character manufacturing die lot. "B6" "B7" or "C2"
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78   errata/trim
79       read-write,unsigned integer
80       32  bit trim value in the EEPROM of the chip. When written, it does not
81       seem to read back. Used for a production problem in the B7 die.
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83       Read allowed for all chips. Only the B7 chips can be written.
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85   errata/trimblanket
86       read-write,yes-no
87       Writing non-zero (=1) puts a default trim value in the chip.  Only  ap‐
88       plied  to the B7 die.  Reading will be true (non-zero) if trim value is
89       the blanket value. Again, only B7 chips will register true,  and  since
90       the  written  trim  values  cannot  be read, this value may have little
91       utility.
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93   errata/trimvalid
94       read-only,yes-no
95       Is the trim value in the valid range? Non-zero if true, which  includes
96       all non-B7 chips.
97

STANDARD PROPERTIES

99   address
100   r_address
101       read-only, ascii
102       The  entire  64-bit  unique  ID. Given as upper case hexadecimal digits
103       (0-9A-F).
104       address starts with the family code
105       r address is the address in reverse order, which is often used in other
106       applications and labeling.
107
108   crc8
109       read-only, ascii
110       The  8-bit error correction portion. Uses cyclic redundancy check. Com‐
111       puted from the preceding 56 bits of the unique ID number. Given as  up‐
112       per case hexadecimal digits (0-9A-F).
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114   family
115       read-only, ascii
116       The  8-bit  family  code. Unique to each type of device. Given as upper
117       case hexadecimal digits (0-9A-F).
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119   id
120   r_id
121       read-only, ascii
122       The 48-bit middle portion of the unique ID number. Does not include the
123       family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
124       r  id is the id in reverse order, which is often used in other applica‐
125       tions and labeling.
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127   locator
128   r_locator
129       read-only, ascii
130       Uses an extension of the 1-wire design from  iButtonLink  company  that
131       associated  1-wire  physical  connections with a unique 1-wire code. If
132       the connection is behind a Link Locator the locator will show a  unique
133       8-byte number (16 character hexadecimal) starting with family code FE.
134       If  no  Link  Locator is between the device and the master, the locator
135       field will be all FF.
136       r locator is the locator in reverse order.
137
138   present (DEPRECATED)
139       read-only, yes-no
140       Is the device currently present on the 1-wire bus?
141
142   type
143       read-only, ascii
144       Part name assigned by Dallas Semi. E.g.  DS2401  Alternative  packaging
145       (iButton vs chip) will not be distiguished.
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DESCRIPTION

148   1-Wire
149       1-wire is a wiring protocol and series of devices designed and manufac‐
150       tured by Dallas Semiconductor, Inc. The bus is  a  low-power  low-speed
151       low-connector scheme where the data line can also provide power.
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153       Each  device  is  uniquely and unalterably numbered during manufacture.
154       There are a wide variety of devices, including memory, sensors  (humid‐
155       ity, temperature, voltage, contact, current), switches, timers and data
156       loggers. More complex devices (like thermocouple sensors) can be  built
157       with  these  basic devices. There are also 1-wire devices that have en‐
158       cryption included.
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160       The 1-wire scheme uses a single bus master and multiple slaves  on  the
161       same  wire.  The bus master initiates all communication. The slaves can
162       be individually discovered and addressed using their unique ID.
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164       Bus masters come in a variety of configurations including serial,  par‐
165       allel, i2c, network or USB adapters.
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167   OWFS design
168       OWFS  is  a  suite of programs that designed to make the 1-wire bus and
169       its devices easily accessible. The underlying principle is to create  a
170       virtual filesystem, with the unique ID being the directory, and the in‐
171       dividual properties of the device are represented as simple files  that
172       can be read and written.
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174       Details  of  the  individual slave or master design are hidden behind a
175       consistent interface. The goal is to provide an easy set of tools for a
176       software  designer  to create monitoring or control applications. There
177       are some performance enhancements in the implementation, including data
178       caching, parallel access to bus masters, and aggregation of device com‐
179       munication. Still the fundamental goal has been ease of use,  flexibil‐
180       ity and correctness rather than speed.
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182   DS18S20 DS1920
183       The DS18S20 (3) is one of several available 1-wire temperature sensors.
184       It has been largely replaced by the DS18B20 (3) and DS1822 (3) as  well
185       as  temperature/vlotage  measurements in the DS2436 (3) and DS2438 (3).
186       For truly versatile temperature measurements, see  the  protean  DS1921
187       [1m(3) Thermachron (3).
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ADDRESSING

190       All  1-wire  devices are factory assigned a unique 64-bit address. This
191       address is of the form:
192
193       Family Code
194              8 bits
195
196       Address
197              48 bits
198
199       CRC    8 bits
200
201       Addressing under OWFS is in hexadecimal, of form:
202
203              01.123456789ABC
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205       where 01 is an example 8-bit family code, and 12345678ABC is an example
206       48 bit address.
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208       The  dot  is  optional,  and the CRC code can included. If included, it
209       must be correct.
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DATASHEET

212       http://pdfserv.maxim-ic.com/en/ds/DS18S20.pdf
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AVAILABILITY

276       http://www.owfs.org
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AUTHOR

279       Paul Alfille (paul.alfille@gmail.com)
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283OWFS Manpage                         2003                           DS18S20(3)