DS2781(3)

1DS2760(3)                    One-Wire File System                    DS2760(3)
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NAME

6       DS2781 - Stand-alone Fuel Gauge IC
7

SYNOPSIS

9   Temperature Voltage Current Memory and Switch.
10       3D     [.]XXXXXXXXXXXX[XX][/[     lock.[0-1|ALL]     |     memory     |
11       pages/page.[0-1|ALL] | PIO | sensed |  temperature  |  vbias  |  vis  |
12       vis_avg | vis_offset | volt | volthours |
13       aef | chgtf | learnf | pmod | porf | sef | uven | uvf |
14       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
15
16   Thermocouple
17       3D    [.]XXXXXXXXXXXX[XX][/[    temperature    |    typeX/range_low   |
18       typeX/range_high | typeX/temperature
19

FAMILY CODE

21       3D
22

SPECIAL PROPERTIES

24   lock.[0-1|ALL]
25       read-write, yes-no
26       Lock either of the two eprom pages to prevent  further  writes.  Appar‐
27       ently setting lock is permanent.
28
29   memory
30       read-write, binary
31       Access  to  the  full  256 byte memory range. Much of this space is re‐
32       served or special use. User space is the page area.
33       See the DATASHEET for a full memory map.
34
35   pages/pages.[0-1|ALL]
36       read-write, binary Two 16 byte areas of memory  for  user  application.
37       The lock property can prevent further alteration.
38       NOTE that the page property is different from the common OWFS implemen‐
39       tation in that all of memory is not accessible.
40
41   PIO
42       write-only, yes-no
43       Controls the PIO pin allowing external switching.
44       Writing "1" turns the PIO pin on (conducting). Writing  "0"  makes  the
45       pin  non-conducting.  The logical state of the voltage can be read with
46       the sensed property. This will reflect the current voltage at the  pin,
47       not the value sent to PIO
48       Note  also  that  PIO  will  also be altered by the power-status of the
49       DS2680 See the datasheet for details.
50
51   sensed
52       read-only, yes-no
53       The logical voltage at the PIO pin. Useful only if the PIO property  is
54       set to "0" (non-conducting).
55       Value will be 0 or 1 depending on the voltage threshold.
56
57   temperature
58       read-only, floating point
59       Temperature  read  by the chip at high resolution (~13 bits). Units are
60       selected from the invoking command line. See owfs(1) or owhttpd(1)  for
61       choices. Default is Celsius.
62       Conversion is continuous.
63
64   vbias
65       read-write, floating point
66       Fixed  offset  applied  to each vis measurement. Used for the volthours
67       value. Units are in Volts.
68       Range -2.0mV to 2.0mV
69
70   vis
71       read-only, floating point
72       Current sensor reading (unknown external resistor). Measures the  volt‐
73       age gradient between the Vis pins. Units are in Volts
74       The  vis  readings  are  integrated  over time to provide the volthours
75       property.
76       The current reading is derived from vis assuming the internal  25  mOhm
77       resistor is employed. There is no way to know this through software.
78
79   vis_avg
80       read-only, floating point
81       Average  current  sensor  reading (unknown external resistor). Measures
82       the voltage gradient between the Vis pins. Units are in Volts
83
84   vis_offset
85       read-write, floating point
86       Offset to vis for current sensor reading (unknown  external  resistor).
87       Units are in Volts
88
89   volt
90       read-only, floating point
91       Voltage  read  at  the  voltage  sensor;. This is separate from the vis
92       voltage that is used for current measurement. Units are Volts
93       Range is between 0 and 4.75V
94
95   volthours
96       read-write, floating point
97       Integral of vis - vbias over time. Units are in volthours
98

THERMOCOUPLE

100   typeX/
101       directory
102       Thermocouple circuit using the DS2781 to read the Seebeck  voltage  and
103       the  reference temperature. Since the type interpretation of the values
104       read depends on the type of thermocouple, the correct directory must be
105       chosen.  Supported thermocouple types include types B, E, J, K, N, R, S
106       and T.
107
108   typeX/range_low typeX/ranges_high
109       read-only, flaoting point
110       The lower and upper temperature  supported  by  this  thermocouple  (at
111       least  by  the conversion routines). In the globally chosen temperature
112       units.
113
114   typeX/temperature
115       read-only, floating point
116       Thermocouple temperature. Requires a voltage  and  temperature  conver‐
117       sion. Returned in globally chosen temperature units.
118       Note:  there  are  two  types of temperature measurements possible. The
119       temperature value in the main device directory is the reference temper‐
120       ature  read  at the chip. The typeX/temperature value is at the thermo‐
121       couple junction, probably remote from the chip.
122

OBSCURE PROPERTIES

124   aef chgtf learnf pmod porf sef uven uvf
125       varies, yes-no
126       Bit flags corresponding to various battery management functions of  the
127       chip. See the DATASHEET for details of the identically named entries.
128       In general, writing "0" corresponds to a 0 bit value, and non-zero cor‐
129       responds to a 1 bit value.
130

STANDARD PROPERTIES

132   address
133   r_address
134       read-only, ascii
135       The entire 64-bit unique ID. Given as  upper  case  hexadecimal  digits
136       (0-9A-F).
137       address starts with the family code
138       r address is the address in reverse order, which is often used in other
139       applications and labeling.
140
141   crc8
142       read-only, ascii
143       The 8-bit error correction portion. Uses cyclic redundancy check.  Com‐
144       puted  from the preceding 56 bits of the unique ID number. Given as up‐
145       per case hexadecimal digits (0-9A-F).
146
147   family
148       read-only, ascii
149       The 8-bit family code. Unique to each type of device.  Given  as  upper
150       case hexadecimal digits (0-9A-F).
151
152   id
153   r_id
154       read-only, ascii
155       The 48-bit middle portion of the unique ID number. Does not include the
156       family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
157       r id is the id in reverse order, which is often used in other  applica‐
158       tions and labeling.
159
160   locator
161   r_locator
162       read-only, ascii
163       Uses  an  extension  of the 1-wire design from iButtonLink company that
164       associated 1-wire physical connections with a unique  1-wire  code.  If
165       the  connection is behind a Link Locator the locator will show a unique
166       8-byte number (16 character hexadecimal) starting with family code FE.
167       If no Link Locator is between the device and the  master,  the  locator
168       field will be all FF.
169       r locator is the locator in reverse order.
170
171   present (DEPRECATED)
172       read-only, yes-no
173       Is the device currently present on the 1-wire bus?
174
175   type
176       read-only, ascii
177       Part  name  assigned by Dallas Semi. E.g.  DS2401 Alternative packaging
178       (iButton vs chip) will not be distiguished.
179

ALARMS

181       None.
182

DESCRIPTION

184   1-Wire
185       1-wire is a wiring protocol and series of devices designed and manufac‐
186       tured  by  Dallas  Semiconductor, Inc. The bus is a low-power low-speed
187       low-connector scheme where the data line can also provide power.
188
189       Each device is uniquely and unalterably  numbered  during  manufacture.
190       There  are a wide variety of devices, including memory, sensors (humid‐
191       ity, temperature, voltage, contact, current), switches, timers and data
192       loggers.  More complex devices (like thermocouple sensors) can be built
193       with these basic devices. There are also 1-wire devices that  have  en‐
194       cryption included.
195
196       The  1-wire  scheme uses a single bus master and multiple slaves on the
197       same wire. The bus master initiates all communication. The  slaves  can
198       be individually discovered and addressed using their unique ID.
199
200       Bus  masters come in a variety of configurations including serial, par‐
201       allel, i2c, network or USB adapters.
202
203   OWFS design
204       OWFS is a suite of programs that designed to make the  1-wire  bus  and
205       its  devices easily accessible. The underlying principle is to create a
206       virtual filesystem, with the unique ID being the directory, and the in‐
207       dividual  properties of the device are represented as simple files that
208       can be read and written.
209
210       Details of the individual slave or master design are  hidden  behind  a
211       consistent interface. The goal is to provide an easy set of tools for a
212       software designer to create monitoring or control  applications.  There
213       are some performance enhancements in the implementation, including data
214       caching, parallel access to bus masters, and aggregation of device com‐
215       munication.  Still the fundamental goal has been ease of use, flexibil‐
216       ity and correctness rather than speed.
217
218   DS2781
219       The DS2781 (3) is a battery charging controller. It has elaborate algo‐
220       rithms for estimating battery capacity.
221
222       A  number of interesting devices can be built with the DS2781 including
223       thermocouples. Support for thermocouples in built  into  the  software,
224       using the embedded thermister as the cold junction temperature.
225

ADDRESSING

227       All  1-wire  devices are factory assigned a unique 64-bit address. This
228       address is of the form:
229
230       Family Code
231              8 bits
232
233       Address
234              48 bits
235
236       CRC    8 bits
237
238       Addressing under OWFS is in hexadecimal, of form:
239
240              01.123456789ABC
241
242       where 01 is an example 8-bit family code, and 12345678ABC is an example
243       48 bit address.
244
245       The  dot  is  optional,  and the CRC code can included. If included, it
246       must be correct.
247

DATASHEET

249       http://pdfserv.maxim-ic.com/en/ds/DS2781.pdf
250

AVAILABILITY

313       http://www.owfs.org
314

AUTHOR

316       Paul Alfille (paul.alfille@gmail.com)
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320OWFS Manpage                         2003                            DS2760(3)