Ubuntu Manpage: DS2781 - Stand-alone Fuel Gauge IC

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NAME

       DS2781 - Stand-alone Fuel Gauge IC

SYNOPSIS

   Temperature Voltage Current Memory and Switch.
       3D  [.]XXXXXXXXXXXX[XX][/[ lock.[0-1|ALL] | memory | pages/page.[0-1|ALL] | PIO | sensed |
       temperature | vbias | vis | vis_avg | vis_offset | volt | volthours |
       aef | chgtf | learnf | pmod | porf | sef | uven | uvf |
       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]

   Thermocouple
       3D   [.]XXXXXXXXXXXX[XX][/[   temperature   |   typeX/range_low   |   typeX/range_high   |
       typeX/temperature

FAMILY CODE

3D

SPECIAL PROPERTIES

lock.[0-1|ALL]
read-write, yes-no
Lock either of the two eprom pages to prevent further writes. Apparently setting lock is
permanent.

memory
read-write, binary
Access to the full 256 byte memory range. Much of this space is reserved or special use.
User space is the page area.
See the DATASHEET for a full memory map.

pages/pages.[0-1|ALL]
read-write, binary Two 16 byte areas of memory for user application. The lock property can
prevent further alteration.
NOTE that the page property is different from the common OWFS implementation in that all
of memory is not accessible.

PIO
write-only, yes-no
Controls the PIO pin allowing external switching.
Writing "1" turns the PIO pin on (conducting). Writing "0" makes the pin non-conducting.
The logical state of the voltage can be read with the sensed property. This will reflect
the current voltage at the pin, not the value sent to PIO
Note also that PIO will also be altered by the power-status of the DS2680 See the
datasheet for details.

sensed
read-only, yes-no
The logical voltage at the PIO pin. Useful only if the PIO property is set to "0" (non-
conducting).
Value will be 0 or 1 depending on the voltage threshold.

temperature
read-only, floating point
Temperature read by the chip at high resolution (~13 bits). Units are selected from the
invoking command line. See owfs(1) or owhttpd(1) for choices. Default is Celsius.
Conversion is continuous.

vbias
read-write, floating point
Fixed offset applied to each vis measurement. Used for the volthours value. Units are in
Volts.
Range -2.0mV to 2.0mV

vis
read-only, floating point
Current sensor reading (unknown external resistor). Measures the voltage gradient between
the Vis pins. Units are in Volts
The vis readings are integrated over time to provide the volthours property.
The current reading is derived from vis assuming the internal 25 mOhm resistor is
employed. There is no way to know this through software.

vis_avg
read-only, floating point
Average current sensor reading (unknown external resistor). Measures the voltage gradient
between the Vis pins. Units are in Volts

vis_offset
read-write, floating point
Offset to vis for current sensor reading (unknown external resistor). Units are in Volts

volt
read-only, floating point
Voltage read at the voltage sensor;. This is separate from the vis voltage that is used
for current measurement. Units are Volts
Range is between 0 and 4.75V

volthours
read-write, floating point
Integral of vis - vbias over time. Units are in volthours

THERMOCOUPLE

   typeX/
       directory
       Thermocouple  circuit  using  the  DS2781  to  read  the Seebeck voltage and the reference
       temperature. Since the type interpretation of the values  read  depends  on  the  type  of
       thermocouple,  the  correct directory must be chosen. Supported thermocouple types include
       types B, E, J, K, N, R, S and T.

   typeX/range_low typeX/ranges_high
       read-only, flaoting point
       The lower and upper temperature supported by this thermocouple (at least by the conversion
       routines). In the globally chosen temperature units.

   typeX/temperature
       read-only, floating point
       Thermocouple  temperature.  Requires  a  voltage  and  temperature conversion. Returned in
       globally chosen temperature units.
       Note: there are two types of temperature measurements possible. The temperature  value  in
       the   main   device  directory  is  the  reference  temperature  read  at  the  chip.  The
       typeX/temperature value is at the thermocouple junction, probably remote from the chip.

OBSCURE PROPERTIES

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

STANDARD PROPERTIES

address
r_address
read-only, ascii
The entire 64-bit unique ID. Given as upper case hexadecimal digits (0-9A-F).
address starts with the family code
r address is the address in reverse order, which is often used in other applications and
labeling.

crc8
read-only, ascii
The 8-bit error correction portion. Uses cyclic redundancy check. Computed from the
preceding 56 bits of the unique ID number. Given as upper case hexadecimal digits (0-9A-
F).

family
read-only, ascii
The 8-bit family code. Unique to each type of device. Given as upper case hexadecimal
digits (0-9A-F).

id
r_id
read-only, ascii
The 48-bit middle portion of the unique ID number. Does not include the family code or
CRC. Given as upper case hexadecimal digits (0-9A-F).
r id is the id in reverse order, which is often used in other applications and labeling.

locator
r_locator
read-only, ascii
Uses an extension of the 1-wire design from iButtonLink company that associated 1-wire
physical connections with a unique 1-wire code. If the connection is behind a Link Locator
the locator will show a unique 8-byte number (16 character hexadecimal) starting with
family code FE.
If no Link Locator is between the device and the master, the locator field will be all FF.
r locator is the locator in reverse order.

present (DEPRECATED)
read-only, yes-no
Is the device currently present on the 1-wire bus?

type
read-only, ascii
Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip)
will not be distiguished.

ALARMS

       None.

DESCRIPTION

1-Wire
1-wire is a wiring protocol and series of devices designed and manufactured by Dallas
Semiconductor, Inc. The bus is a low-power low-speed low-connector scheme where the data
line can also provide power.

Each device is uniquely and unalterably numbered during manufacture. There are a wide
variety of devices, including memory, sensors (humidity, temperature, voltage, contact,
current), switches, timers and data loggers. More complex devices (like thermocouple
sensors) can be built with these basic devices. There are also 1-wire devices that have
encryption included.

The 1-wire scheme uses a single bus master and multiple slaves on the same wire. The bus
master initiates all communication. The slaves can be individually discovered and
addressed using their unique ID.

Bus masters come in a variety of configurations including serial, parallel, i2c, network
or USB adapters.

OWFS design
OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily
accessible. The underlying principle is to create a virtual filesystem, with the unique ID
being the directory, and the individual properties of the device are represented as simple
files that can be read and written.

Details of the individual slave or master design are hidden behind a consistent interface.
The goal is to provide an easy set of tools for a software designer to create monitoring
or control applications. There are some performance enhancements in the implementation,
including data caching, parallel access to bus masters, and aggregation of device
communication. Still the fundamental goal has been ease of use, flexibility and
correctness rather than speed.

DS2781
The DS2781 (3) is a battery charging controller. It has elaborate algorithms for
estimating battery capacity.

A number of interesting devices can be built with the DS2781 including thermocouples.
Support for thermocouples in built into the software, using the embedded thermister as the
cold junction temperature.

ADDRESSING

       All  1-wire  devices  are factory assigned a unique 64-bit address. This address is of the
       form:

       Family Code
              8 bits

       Address
              48 bits

       CRC    8 bits

       Addressing under OWFS is in hexadecimal, of form:

              01.123456789ABC

       where 01 is an example 8-bit family code, and 12345678ABC is an example 48 bit address.

       The dot is optional, and the CRC code can included. If included, it must be correct.

DATASHEET

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

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)