Ubuntu Manpage: DS1825 - Programmable Resolution 1-Wire Digital Thermometer with ID

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NAME

       DS1825 - Programmable Resolution 1-Wire Digital Thermometer with ID

       MAX31826
              - Digital Temperature Sensor with 1Kb Lockable EEPROM

       MAX31850 MAX31851
              - Cold-Junction Compensated Thermocouple

SYNOPSIS

   Thermometer with hardware address pins (DS1825)
       3B  [.]XXXXXXXXXXXX[XX][/[  fasttemp  |  temperature  |  temperature9  |  temperature10 | temperature11 |
       temperature12 | latesttemp | power | prog_addr | temphigh | templow | tempres | address |  crc8  |  id  |
       locator | r_address | r_id | r_locator | type ]]

   Digital Temperature Sensor with 1Kb Lockable EEPROM (MAX31826)
       3B [.]XXXXXXXXXXXX[XX][/[ temperature | latesttemp | power | memory | pages/page.[0-15|ALL] | prog_addr |
       address | crc8 | id | locator | r_address | r_id | r_locator | type ]]

   Cold-Junction Compensated Thermocouple (MAX31850 and MAX31851)
       3B [.]XXXXXXXXXXXX[XX][/[ temperature | latesttemp | thermocouple | fault | open_circuit | ground_short |
       vdd_short | power | prog_addr | address | crc8 | id | locator | r_address | r_id | r_locator | type ]]

FAMILY CODE

3B

SPECIAL PROPERTIES

power
read-only,yes-no
Is the chip powered externally (=1) or from the parasitically from the data bus (=0)?

prog_addr
read-only, 0-15
A distiguishing feature of the DS1825 (3) is the ability to set hardware pins for an address (0-15). This
is an alternative to the unique 64-bit address that is set in the factory.

temperature
read-only, floating point
Measured temperature with 12 bit resolution.

For the MAX31850 MAX 31851 this is the cold-junction temperature -- the temperature at the chip. See
thermocouple

temperature9 temperature10 temperature11 temperature12
read-only, floating point ( DS1825 only)

Measured temperature at 9 to 12 bit resolution. There is a tradeoff of time versus accuracy in the
temperature measurement.

The MAX31826 MAX31850 MAX31851 measure all temperatures at 12 bit resoltion and will return that
resolution to all the possible temperature properties.

latesttemp
read-only, floating point
Measured temperature at 9 to 12 bit resolution, depending on the resolution of the latest conversion on
this chip. Reading this node will never trigger a temperature conversion. Intended for use in conjunction
with /simultaneous/temperature.

fasttemp
read-only, floating point
Equivalent to temperature9

thermocouple
read-only, floating point ( MAX31850 MAX31851 only)

Measured temperature of the thermocouple at 16bit resolution. Cold-junction temperature compensated.

The actual thermocouple type used is set by the selected chip type, and is not discoverable in software.

TEMPERATURE ALARM LIMITS

       When  the  device  exceeds  either  temphigh  or templow temperature threshold the device is in the alarm
       state, and will appear in the alarm directory. This provides an easy way to poll  for  temperatures  that
       are unsafe, especially if simultaneous temperature conversion is done.

       Units  for  the  temperature  alarms  are  in  the  same  temperature  scale that was set for temperature
       measurements.

       Temperature thresholds are stored in non-volatile memory and persist until  changed,  even  if  power  is
       lost.

   temphigh
       read-write, integer
       Shows or sets the lower limit for the high temperature alarm state.

   templow
       read-write, integer
       Shows or sets the upper limit for the low temperature alarm state.

       The MAX31826 does NOT have temperature thresholds and temperature alarm.

TEMPERATURE RESOLUTION DEFAULT VALUE

   tempres
       read-write, integer
       The  device  employs  a  non-volatile memory to store the default temperature resolution (9, 10, 11 or 12
       bits) to be applied after power-up. This is useful  if  you  use  simultaneous  temperature  conversions.
       Reading  this  node  gives  you  the value stored in the non-volatile memory. Writing sets a new power-on
       resolution value.

       As a side effect, reading this node resets the temperature resolution used  by  simultaneous  temperature
       conversions  to its power-on value. It also affects the resolution value used by latesttemp, to scale the
       latest conversion value, so make sure to re-sample the  temperature  before  accessing  latesttemp  after
       writing or reading the tempres value.

MEMORY

       Only the MAX31826 supports memory functions.

   pages/page.0 .. pages/page.15 pages/page.ALL
       read/write, binary
       EEPROM memory pages of 8 bytes each. See the datasheet about locking contents.

   memory
       read/write, binary
       EEPROM memory of 128 bytes. See the datasheet about locking contents.

FAULT REPORTING

       Only the MAX31850 MAX31851 supports fault reporting.

   fault
       read-only, yes-no
       Fault in last thermocouple conversion

   open_circuit
       read-only, yes-no
       Thermocouple leads disconnected.

   ground_short
       read-only, yes-no
       Thermocouple lead shorted to ground.

   vdd_short
       read-only, yes-no
       Thermocouple lead shorted to supply voltage.

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.

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.

DS1825
The DS1825 (3) is one of several available 1-wire temperature sensors. Alternatives are the DS18S20 (3),
DS18B20 (3), and DS1822 (3) as well as temperature/voltage measurements in the DS2436 (3) and DS2438 (3).
For truly versatile temperature measurements, see the protean DS1921 (3) Thermachron (3).

The DS1825 (3) can select between 4 resolutionsspanning the fastest/roughest and slowest/best.

MAX31826
The MAX31826 shares a family code with the DS1825 but has differences in some of its functions.

The MAX31826 has 128 btes of EEPROM memory (as 16 pages of 8 bytes) while the DS1825 has no memory
available.

The MAX31826 measures temperature at 12 bit resolution as fast as the DS1825's lowest resolution (and
always uses 12-bit resolution). On the other hand it has no temperature thresholds or alarm function.

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.

       Both  the  MAX31826  and  the  DS1825  allow  hardware selection of part of the address, which can assist
       selecting between chips is some circuit designs.

DATASHEET

       DS1825 http://pdfserv.maxim-ic.com/en/ds/DS1825.pdf

       MAX31826
              http://datasheets.maxim-ic.com/en/ds/MAX31826.pdf

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)