MAX31851(3)

1DS1825(3)                    One-Wire File System                    DS1825(3)
2
3
4

NAME

6       DS1825 - Programmable Resolution 1-Wire Digital Thermometer with ID
7
8       MAX31826
9              - Digital Temperature Sensor with 1Kb Lockable EEPROM
10
11       MAX31850 MAX31851
12              - Cold-Junction Compensated Thermocouple
13

SYNOPSIS

15   Thermometer with hardware address pins (DS1825)
16       3B  [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9 | tem‐
17       perature10 | temperature11 |  temperature12  |  latesttemp  |  power  |
18       prog_addr  | temphigh | templow | tempres | address | crc8 | id | loca‐
19       tor | r_address | r_id | r_locator | type ]]
20
21   Digital Temperature Sensor with 1Kb Lockable EEPROM (MAX31826)
22       3B [.]XXXXXXXXXXXX[XX][/[ temperature | latesttemp | power |  memory  |
23       pages/page.[0-15|ALL]  |  prog_addr  |  address | crc8 | id | locator |
24       r_address | r_id | r_locator | type ]]
25
26   Cold-Junction Compensated Thermocouple (MAX31850 and MAX31851)
27       3B [.]XXXXXXXXXXXX[XX][/[ temperature |  latesttemp  |  thermocouple  |
28       fault  |  open_circuit | ground_short | vdd_short | power | prog_addr |
29       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
30

FAMILY CODE

32       3B
33

SPECIAL PROPERTIES

35   power
36       read-only,yes-no
37       Is the chip powered externally (=1) or from the parasitically from  the
38       data bus (=0)?
39
40   prog_addr
41       read-only, 0-15
42       A  distiguishing  feature of the DS1825 (3) is the ability to set hard‐
43       ware pins for an address (0-15). This is an alternative to  the  unique
44       64-bit address that is set in the factory.
45
46   temperature
47       read-only, floating point
48       Measured temperature with 12 bit resolution.
49
50       For the MAX31850 MAX 31851 this is the cold-junction temperature -- the
51       temperature at the chip. See thermocouple
52
53   temperature9 temperature10 temperature11 temperature12
54       read-only, floating point ( DS1825 only)
55
56       Measured temperature at 9 to 12 bit resolution. There is a tradeoff  of
57       time versus accuracy in the temperature measurement.
58
59       The  MAX31826  MAX31850  MAX31851  measure  all  temperatures at 12 bit
60       resoltion and will return that resolution to all the possible  tempera‐
61       ture properties.
62
63   latesttemp
64       read-only, floating point
65       Measured  temperature at 9 to 12 bit resolution, depending on the reso‐
66       lution of the latest conversion on this chip. Reading  this  node  will
67       never trigger a temperature conversion. Intended for use in conjunction
68       with /simultaneous/temperature.
69
70   fasttemp
71       read-only, floating point
72       Equivalent to temperature9
73
74   thermocouple
75       read-only, floating point ( MAX31850 MAX31851 only)
76
77       Measured temperature of the thermocouple  at  16bit  resolution.  Cold-
78       junction temperature compensated.
79
80       The actual thermocouple type used is set by the selected chip type, and
81       is not discoverable in software.
82

TEMPERATURE ALARM LIMITS

84       When the device exceeds either temphigh or templow temperature  thresh‐
85       old  the  device  is  in  the alarm state, and will appear in the alarm
86       directory. This provides an easy way to poll for temperatures that  are
87       unsafe, especially if simultaneous temperature conversion is done.
88
89       Units for the temperature alarms are in the same temperature scale that
90       was set for temperature measurements.
91
92       Temperature thresholds are stored in non-volatile  memory  and  persist
93       until changed, even if power is lost.
94
95   temphigh
96       read-write, integer
97       Shows or sets the lower limit for the high temperature alarm state.
98
99   templow
100       read-write, integer
101       Shows or sets the upper limit for the low temperature alarm state.
102
103       The  MAX31826  does  NOT  have  temperature  thresholds and temperature
104       alarm.
105

TEMPERATURE RESOLUTION DEFAULT VALUE

107   tempres
108       read-write, integer
109       The device employs a non-volatile memory to store the default  tempera‐
110       ture  resolution  (9,  10, 11 or 12 bits) to be applied after power-up.
111       This is useful if you use simultaneous temperature conversions. Reading
112       this  node gives you the value stored in the non-volatile memory. Writ‐
113       ing sets a new power-on resolution value.
114
115       As a side effect, reading this node resets the  temperature  resolution
116       used  by simultaneous temperature conversions to its power-on value. It
117       also affects the resolution value used by latesttemp, to scale the lat‐
118       est  conversion value, so make sure to re-sample the temperature before
119       accessing latesttemp after writing or reading the tempres value.
120

MEMORY

122       Only the MAX31826 supports memory functions.
123
124   pages/page.0 .. pages/page.15 pages/page.ALL
125       read/write, binary
126       EEPROM memory pages of 8 bytes each. See the  datasheet  about  locking
127       contents.
128
129   memory
130       read/write, binary
131       EEPROM memory of 128 bytes. See the datasheet about locking contents.
132

FAULT REPORTING

134       Only the MAX31850 MAX31851 supports fault reporting.
135
136   fault
137       read-only, yes-no
138       Fault in last thermocouple conversion
139
140   open_circuit
141       read-only, yes-no
142       Thermocouple leads disconnected.
143
144   ground_short
145       read-only, yes-no
146       Thermocouple lead shorted to ground.
147
148   vdd_short
149       read-only, yes-no
150       Thermocouple lead shorted to supply voltage.
151

STANDARD PROPERTIES

153   address
154   r_address
155       read-only, ascii
156       The  entire  64-bit  unique  ID. Given as upper case hexidecimal digits
157       (0-9A-F).
158       address starts with the family code
159       r address is the address in reverse order, which is often used in other
160       applications and labeling.
161
162   crc8
163       read-only, ascii
164       The  8-bit error correction portion. Uses cyclic redundancy check. Com‐
165       puted from the preceding 56 bits of the  unique  ID  number.  Given  as
166       upper case hexidecimal digits (0-9A-F).
167
168   family
169       read-only, ascii
170       The  8-bit  family  code. Unique to each type of device. Given as upper
171       case hexidecimal digits (0-9A-F).
172
173   id
174   r_id
175       read-only, ascii
176       The 48-bit middle portion of the unique ID number. Does not include the
177       family code or CRC. Given as upper case hexidecimal digits (0-9A-F).
178       r  id is the id in reverse order, which is often used in other applica‐
179       tions and labeling.
180
181   locator
182   r_locator
183       read-only, ascii
184       Uses an extension of the 1-wire design from  iButtonLink  company  that
185       associated  1-wire  physical  connections with a unique 1-wire code. If
186       the connection is behind a Link Locator the locator will show a  unique
187       8-byte number (16 character hexidecimal) starting with family code FE.
188       If  no  Link  Locator is between the device and the master, the locator
189       field will be all FF.
190       r locator is the locator in reverse order.
191
192   present (DEPRECATED)
193       read-only, yes-no
194       Is the device currently present on the 1-wire bus?
195
196   type
197       read-only, ascii
198       Part name assigned by Dallas Semi. E.g.  DS2401  Alternative  packaging
199       (iButton vs chip) will not be distiguished.
200

DESCRIPTION

202   1-Wire
203       1-wire is a wiring protocol and series of devices designed and manufac‐
204       tured by Dallas Semiconductor, Inc. The bus is  a  low-power  low-speed
205       low-connector scheme where the data line can also provide power.
206
207       Each  device  is  uniquely and unalterably numbered during manufacture.
208       There are a wide variety of devices, including memory, sensors  (humid‐
209       ity, temperature, voltage, contact, current), switches, timers and data
210       loggers. More complex devices (like thermocouple sensors) can be  built
211       with  these  basic  devices.  There  are  also 1-wire devices that have
212       encryption included.
213
214       The 1-wire scheme uses a single bus master and multiple slaves  on  the
215       same  wire.  The bus master initiates all communication. The slaves can
216       be individually discovered and addressed using their unique ID.
217
218       Bus masters come in a variety of configurations including serial,  par‐
219       allel, i2c, network or USB adapters.
220
221   OWFS design
222       OWFS  is  a  suite of programs that designed to make the 1-wire bus and
223       its devices easily accessible. The underlying principle is to create  a
224       virtual  filesystem,  with  the  unique ID being the directory, and the
225       individual properties of the device are  represented  as  simple  files
226       that can be read and written.
227
228       Details  of  the  individual slave or master design are hidden behind a
229       consistent interface. The goal is to provide an easy set of tools for a
230       software  designer  to create monitoring or control applications. There
231       are some performance enhancements in the implementation, including data
232       caching, parallel access to bus masters, and aggregation of device com‐
233       munication. Still the fundemental goal has been ease of use,  flexibil‐
234       ity and correctness rather than speed.
235
236   DS1825
237       The  DS1825 (3) is one of several available 1-wire temperature sensors.
238       Alternatives are the DS18S20 (3), DS18B20 (3), and DS1822 (3)  as  well
239       as  temperature/voltage  measurements in the DS2436 (3) and DS2438 (3).
240       For truly versatile temperature measurements, see  the  protean  DS1921
241       [1m(3) Thermachron (3).
242
243       The   DS1825   (3)   can   select  between  4  resolutionsspanning  the
244       fastest/roughest and slowest/best.
245
246   MAX31826
247       The MAX31826 shares a family code with the DS1825 but  has  differences
248       in some of its functions.
249
250       The  MAX31826  has  128  btes of EEPROM memory (as 16 pages of 8 bytes)
251       while the DS1825 has no memory available.
252
253       The MAX31826 measures temperature at 12 bit resolution as fast  as  the
254       DS1825's  lowest resolution (and always uses 12-bit resolution). On the
255       other hand it has no temperature thresholds or alarm function.
256

ADDRESSING

258       All 1-wire devices are factory assigned a unique 64-bit  address.  This
259       address is of the form:
260
261       Family Code
262              8 bits
263
264       Address
265              48 bits
266
267       CRC    8 bits
268
269       Addressing under OWFS is in hexidecimal, of form:
270
271              01.123456789ABC
272
273       where 01 is an example 8-bit family code, and 12345678ABC is an example
274       48 bit address.
275
276       The dot is optional, and the CRC code can  included.  If  included,  it
277       must be correct.
278
279       Both  the  MAX31826  and the DS1825 allow hardware selection of part of
280       the address, which can assist selecting between chips is  some  circuit
281       designs.
282

DATASHEET

284       DS1825 http://pdfserv.maxim-ic.com/en/ds/DS1825.pdf
285
286       MAX31826
287              http://datasheets.maxim-ic.com/en/ds/MAX31826.pdf
288

AVAILABILITY

350       http://www.owfs.org
351

AUTHOR

353       Paul Alfille (paul.alfille@gmail.com)
354
355
356
357OWFS Manpage                         2006                            DS1825(3)