Ubuntu Manpage: DS2740 - High-Precision Coulomb Counter

Provided by: owfs-doc_2.8p15-1ubuntu4_all

NAME

       DS2740 - High-Precision Coulomb Counter

SYNOPSIS

       Voltage and Switch

       36 [.]XXXXXXXXXXXX[XX][/[ memory | PIO | sensed | vis | vis_B | volthours |
       smod |
       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]

FAMILY CODE

SPECIAL PROPERTIES

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.

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 DS2670 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.

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_B
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 vis_B is from a different tuning of the DS2740 (3) chip with faster sampling and lower
resolution. There is no way to know this through software.

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

OBSCURE PROPERTIES

   smod
       read-write, 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.
       Default power-on state for the corresponding properties.

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 priciple 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.

DS2740
The DS2740 (3) is a class of battery charging controllers. This chip measures voltage and
volthours, and has a pin that can be used for control.

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/DS2740.pdf

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)