Ubuntu Manpage: DS2740 - High-Precision Coulomb Counter

name
synopsis
family code
special properties
obscure properties
standard properties
alarms
description
addressing
datasheet
see also
availability
author

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 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 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 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/DS2740.pdf

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)