DS28EA00(3)

1DS28EA00(3)                  One-Wire File System                  DS28EA00(3)
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NAME

6       DS28EA00 - 1-Wire Digital Thermometer with Sequence Detect and PIO
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SYNOPSIS

9       Thermometer, PIO and Chain.
10
11       42  [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9 | tem‐
12       perature10 | temperature11 | temperature12 | latesttemp | die | power |
13       temphigh  | templow | tempres | PIO.A|B|ALL.BYTE | latch.A|B|ALL.BYTE |
14       sensed.A|B|ALL.BYTE
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16       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
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FAMILY CODE

19       42
20

SPECIAL PROPERTIES

22   power
23       read-only,yes-no
24       Is the chip powered externally (=1) or from the parasitically from  the
25       data bus (=0)?
26

TEMPERATURE PROPERTIES

28   temperature
29       read-only, floating point
30       Measured temperature with 12 bit resolution.
31
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.
36
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.
43
44   fasttemp
45       read-only, floating point
46       Equivalent to temperature9
47

PIO PROPERTIES

49   PIO.A|B|ALL|BYTE
50       read-write, yes-no
51       Two channels of sensors/switches. We use the logical raqther than elet‐
52       rical interpretation: 0=off (non-conducting)  1=on  (conducting  --  to
53       ground)
54
55       The PIO channels are alternatively used for the sequence-detect (chain)
56       mode.
57
58       Reading sensed gives the inverse value of the cooresponding PIO.
59
60       Reading PIO gives the actual pin values. Use the latch property to  see
61       how the pin is set.
62
63   latch.A|B|ALL|BYTE
64       read-only, yes-no
65       Set (intended) va;ue of the PIO pins.
66
67   sensed.A|B|ALL|BYTE
68       read-only, yes-no
69       Actual logical level at the PIO pins.
70

SPECIAL PROPERTIES

72   power
73       read-only,yes-no
74       Is  the chip powered externally (=1) or from the parasitically from the
75       data bus (=0)?
76

TEMPERATURE ALARM LIMITS

78       When the device exceeds either temphigh or templow temperature  thresh‐
79       old  the  device  is  in  the alarm state, and will appear in the alarm
80       directory. This provides an easy way to poll for temperatures that  are
81       unsafe, especially if simultaneous temperature conversion is done.
82
83       Units for the temperature alarms are in the same temperature scale that
84       was set for temperature measurements.
85
86       Temperature thresholds are stored in non-volatile  memory  and  persist
87       until changed, even if power is lost.
88
89   temphigh
90       read-write, integer
91       Shows or sets the lower limit for the high temperature alarm state.
92
93   templow
94       read-write, integer
95       Shows or sets the upper limit for the low temperature alarm state.
96

TEMPERATURE RESOLUTION DEFAULT VALUE

98   tempres
99       read-write, integer
100       The  device employs a non-volatile memory to store the default tempera‐
101       ture resolution (9, 10, 11 or 12 bits) to be  applied  after  power-up.
102       This is useful if you use simultaneous temperature conversions. Reading
103       this node gives you the value stored in the non-volatile memory.  Writ‐
104       ing sets a new power-on resolution value.
105
106       As  a  side effect, reading this node resets the temperature resolution
107       used by simultaneous temperature conversions to its power-on value.  It
108       also affects the resolution value used by latesttemp, to scale the lat‐
109       est conversion value, so make sure to re-sample the temperature  before
110       accessing latesttemp after writing or reading the tempres value.
111

STANDARD PROPERTIES

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

162   1-Wire
163       1-wire is a wiring protocol and series of devices designed and manufac‐
164       tured by Dallas Semiconductor, Inc. The bus is  a  low-power  low-speed
165       low-connector scheme where the data line can also provide power.
166
167       Each  device  is  uniquely and unalterably numbered during manufacture.
168       There are a wide variety of devices, including memory, sensors  (humid‐
169       ity, temperature, voltage, contact, current), switches, timers and data
170       loggers. More complex devices (like thermocouple sensors) can be  built
171       with  these  basic  devices.  There  are  also 1-wire devices that have
172       encryption included.
173
174       The 1-wire scheme uses a single bus master and multiple slaves  on  the
175       same  wire.  The bus master initiates all communication. The slaves can
176       be individually discovered and addressed using their unique ID.
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178       Bus masters come in a variety of configurations including serial,  par‐
179       allel, i2c, network or USB adapters.
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181   OWFS design
182       OWFS  is  a  suite of programs that designed to make the 1-wire bus and
183       its devices easily accessible. The underlying principle is to create  a
184       virtual  filesystem,  with  the  unique ID being the directory, and the
185       individual properties of the device are  represented  as  simple  files
186       that can be read and written.
187
188       Details  of  the  individual slave or master design are hidden behind a
189       consistent interface. The goal is to provide an easy set of tools for a
190       software  designer  to create monitoring or control applications. There
191       are some performance enhancements in the implementation, including data
192       caching, parallel access to bus masters, and aggregation of device com‐
193       munication. Still the fundemental goal has been ease of use,  flexibil‐
194       ity and correctness rather than speed.
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196   DS28EA00
197       The  DS28EA00  (3)  is one of several available 1-wire temperature sen‐
198       sors. It is the replacement for the DS18S20 (3) Alternatives are DS1822
199       [1m(3)  as  well as temperature/vlotage measurements in the DS2436 (3) and
200       DS2438 (3).  For truly versatile temperature measurements, see the pro‐
201       tean DS1921 (3) Thermachron (3).
202       The DS28EA00 has special switch/sequence detect properties. In sequence
203       mode, the PIO pins are daisy-chained to the next DS28EA00, allowing the
204       system to step through the physical sequence of the DS28EA00s.
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ADDRESSING

207       All  1-wire  devices are factory assigned a unique 64-bit address. This
208       address is of the form:
209
210       Family Code
211              8 bits
212
213       Address
214              48 bits
215
216       CRC    8 bits
217
218       Addressing under OWFS is in hexidecimal, of form:
219
220              01.123456789ABC
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222       where 01 is an example 8-bit family code, and 12345678ABC is an example
223       48 bit address.
224
225       The  dot  is  optional,  and the CRC code can included. If included, it
226       must be correct.
227

DATASHEET

229       http://pdfserv.maxim-ic.com/en/ds/DS28EA00.pdf
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AVAILABILITY

292       http://www.owfs.org
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AUTHOR

295       Paul Alfille (paul.alfille@gmail.com)
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299OWFS Manpage                         2003                          DS28EA00(3)