DS2740(3)

1DS2740(3)                    One-Wire File System                    DS2740(3)
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3
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NAME

6       DS2740 - High-Precision Coulomb Counter
7

SYNOPSIS

9       Voltage and Switch
10
11       36  [.]XXXXXXXXXXXX[XX][/[  memory  |  PIO  |  sensed  |  vis | vis_B |
12       volthours |
13       smod |
14       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
15

FAMILY CODE

17       36
18

SPECIAL PROPERTIES

20   memory
21       read-write, binary
22       Access to the full 256 byte memory range. Much of  this  space  is  re‐
23       served or special use. User space is the page area.
24       See the DATASHEET for a full memory map.
25
26   PIO
27       write-only, yes-no
28       Controls the PIO pin allowing external switching.
29       Writing  "1"  turns  the PIO pin on (conducting). Writing "0" makes the
30       pin non-conducting.  The logical state of the voltage can be read  with
31       the  sensed property. This will reflect the current voltage at the pin,
32       not the value sent to PIO
33       Note also that PIO will also be altered  by  the  power-status  of  the
34       DS2670 See the datasheet for details.
35
36   sensed
37       read-only, yes-no
38       The  logical voltage at the PIO pin. Useful only if the PIO property is
39       set to "0" (non-conducting).
40       Value will be 0 or 1 depending on the voltage threshold.
41
42   vis
43       read-only, floating point
44       Current sensor reading (unknown external resistor). Measures the  volt‐
45       age gradient between the Vis pins. Units are in Volts
46       The  vis  readings  are  integrated  over time to provide the volthours
47       property.
48       The current reading is derived from vis assuming the internal  25  mOhm
49       resistor is employed. There is no way to know this through software.
50
51   vis_B
52       read-only, floating point
53       Current  sensor reading (unknown external resistor). Measures the volt‐
54       age gradient between the Vis pins. Units are in Volts
55       The vis readings are integrated over  time  to  provide  the  volthours
56       property.
57       The vis_B is from a different tuning of the DS2740 [4m(3) chip with faster
58       sampling and lower resolution.  There is no way to  know  this  through
59       software.
60
61   volthours
62       read-write, floating point
63       Integral of vis over time. Units are in volthours
64

OBSCURE PROPERTIES

66   smod
67       read-write, yes-no
68       Bit  flags corresponding to various battery management functions of the
69       chip. See the DATASHEET for details of the identically named entries.
70       In general, writing "0" corresponds to a 0 bit value, and non-zero cor‐
71       responds to a 1 bit value.
72       Default power-on state for the corresponding properties.
73

STANDARD PROPERTIES

75   address
76   r_address
77       read-only, ascii
78       The  entire  64-bit  unique  ID. Given as upper case hexadecimal digits
79       (0-9A-F).
80       address starts with the family code
81       r address is the address in reverse order, which is often used in other
82       applications and labeling.
83
84   crc8
85       read-only, ascii
86       The  8-bit error correction portion. Uses cyclic redundancy check. Com‐
87       puted from the preceding 56 bits of the unique ID number. Given as  up‐
88       per case hexadecimal digits (0-9A-F).
89
90   family
91       read-only, ascii
92       The  8-bit  family  code. Unique to each type of device. Given as upper
93       case hexadecimal digits (0-9A-F).
94
95   id
96   r_id
97       read-only, ascii
98       The 48-bit middle portion of the unique ID number. Does not include the
99       family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
100       r  id is the id in reverse order, which is often used in other applica‐
101       tions and labeling.
102
103   locator
104   r_locator
105       read-only, ascii
106       Uses an extension of the 1-wire design from  iButtonLink  company  that
107       associated  1-wire  physical  connections with a unique 1-wire code. If
108       the connection is behind a Link Locator the locator will show a  unique
109       8-byte number (16 character hexadecimal) starting with family code FE.
110       If  no  Link  Locator is between the device and the master, the locator
111       field will be all FF.
112       r locator is the locator in reverse order.
113
114   present (DEPRECATED)
115       read-only, yes-no
116       Is the device currently present on the 1-wire bus?
117
118   type
119       read-only, ascii
120       Part name assigned by Dallas Semi. E.g.  DS2401  Alternative  packaging
121       (iButton vs chip) will not be distiguished.
122

ALARMS

124       None.
125

DESCRIPTION

127   1-Wire
128       1-wire is a wiring protocol and series of devices designed and manufac‐
129       tured by Dallas Semiconductor, Inc. The bus is  a  low-power  low-speed
130       low-connector scheme where the data line can also provide power.
131
132       Each  device  is  uniquely and unalterably numbered during manufacture.
133       There are a wide variety of devices, including memory, sensors  (humid‐
134       ity, temperature, voltage, contact, current), switches, timers and data
135       loggers. More complex devices (like thermocouple sensors) can be  built
136       with  these  basic devices. There are also 1-wire devices that have en‐
137       cryption included.
138
139       The 1-wire scheme uses a single bus master and multiple slaves  on  the
140       same  wire.  The bus master initiates all communication. The slaves can
141       be individually discovered and addressed using their unique ID.
142
143       Bus masters come in a variety of configurations including serial,  par‐
144       allel, i2c, network or USB adapters.
145
146   OWFS design
147       OWFS  is  a  suite of programs that designed to make the 1-wire bus and
148       its devices easily accessible. The underlying principle is to create  a
149       virtual filesystem, with the unique ID being the directory, and the in‐
150       dividual properties of the device are represented as simple files  that
151       can be read and written.
152
153       Details  of  the  individual slave or master design are hidden behind a
154       consistent interface. The goal is to provide an easy set of tools for a
155       software  designer  to create monitoring or control applications. There
156       are some performance enhancements in the implementation, including data
157       caching, parallel access to bus masters, and aggregation of device com‐
158       munication. Still the fundamental goal has been ease of use,  flexibil‐
159       ity and correctness rather than speed.
160
161   DS2740
162       The  DS2740  (3)  is a class of battery charging controllers. This chip
163       measures voltage and volthours, and has a pin that can be used for con‐
164       trol.
165

ADDRESSING

167       All  1-wire  devices are factory assigned a unique 64-bit address. This
168       address is of the form:
169
170       Family Code
171              8 bits
172
173       Address
174              48 bits
175
176       CRC    8 bits
177
178       Addressing under OWFS is in hexadecimal, of form:
179
180              01.123456789ABC
181
182       where 01 is an example 8-bit family code, and 12345678ABC is an example
183       48 bit address.
184
185       The  dot  is  optional,  and the CRC code can included. If included, it
186       must be correct.
187

DATASHEET

189       http://pdfserv.maxim-ic.com/en/ds/DS2740.pdf
190

AVAILABILITY

253       http://www.owfs.org
254

AUTHOR

256       Paul Alfille (paul.alfille@gmail.com)
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260OWFS Manpage                         2003                            DS2740(3)