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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 hexidecimal 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 hexidecimal digits (0-9A-F).

   family
       read-only, ascii
       The 8-bit family code. Unique to each type of device. Given as upper case hexidecimal 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 hexidecimal 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 hexidecimal) 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  fundemental  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 hexidecimal, 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

SEE ALSO

   Programs
       owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1) owwrite (1) owpresent (1) owtap (1)

   Configuration and testing
       owfs (5) owtap (1) owmon (1)

   Language bindings
       owtcl (3) owperl (3) owcapi (3)

   Clocks
       DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)

   ID
       DS2401 (3) DS2411 (3) DS1990A (3)

   Memory
       DS1982  (3)  DS1985  (3)  DS1986  (3)  DS1991 (3) DS1992 (3) DS1993 (3) DS1995 (3) DS1996 (3) DS2430A (3)
       DS2431 (3) DS2433 (3) DS2502 (3) DS2506 (3) DS28E04 (3) DS28EC20 (3)

   Switches
       DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)

   Temperature
       DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3) DS1921 (3) DS1821  (3)  DS28EA00  (3)
       DS28E04  (3) EDS0064 (3) EDS0065 (3) EDS0066 (3) EDS0067 (3) EDS0068 (3) EDS0071 (3) EDS0072 (3) MAX31826
       (3)

   Humidity
       DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)

   Voltage
       DS2450 (3)

   Resistance
       DS2890 (3)

   Multifunction (current, voltage, temperature)
       DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3) DS2760 (3) DS2770 (3) DS2780 (3) DS2781
       (3) DS2788 (3) DS2784 (3)

   Counter
       DS2423 (3)

   LCD Screen
       LCD (3) DS2408 (3)

   Crypto
       DS1977 (3)

   Pressure
       DS2406 (3) TAI8570 EDS0066 (3) EDS0068 (3)

   Moisture
       EEEF (3) DS2438 (3)

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)