DS1825 - Programmable Resolution 1-Wire Digital Thermometer with ID

Addressing

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

       FamilyCode
              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.

Author

       Paul Alfille (paul.alfille@gmail.com)

OWFS Manpage                                          2006                                             DS1825(3)

Availability

http://www.owfs.org

Datasheet

DS1825http://pdfserv.maxim-ic.com/en/ds/DS1825.pdfMAX31826http://datasheets.maxim-ic.com/en/ds/MAX31826.pdf

Description

1-Wire1-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 busmaster 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.

OWFSdesignOWFS 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.

Family Code

3B

Fault Reporting

       Only the MAX31850MAX31851 supports fault reporting.

   faultread-only,yes-no
       Fault in last thermocouple conversion

   open_circuitread-only,yes-no
       Thermocouple leads disconnected.

   ground_shortread-only,yes-no
       Thermocouple lead shorted to ground.

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

Memory

       Only the MAX31826 supports memory functions.

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

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

Name

DS1825 - Programmable Resolution 1-Wire Digital Thermometer with ID

       MAX31826
              - Digital Temperature Sensor with 1Kb Lockable EEPROM

       MAX31850MAX31851
              - Cold-Junction Compensated Thermocouple

Special Properties

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

prog_addrread-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.

temperatureread-only,floatingpoint
Measured temperature with 12 bit resolution.

For the MAX31850MAX31851 this is the cold-junctiontemperature -- the temperature at the chip. See
thermocoupletemperature9temperature10temperature11temperature12read-only,floatingpoint ( DS1825 only)

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

The MAX31826MAX31850MAX31851 measure all temperatures at 12 bit resoltion and will return that
resolution to all the possible temperature properties.

latesttempread-only,floatingpoint
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.fasttempread-only,floatingpoint
Equivalent to temperature9thermocoupleread-only,floatingpoint ( MAX31850MAX31851 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.

Standard Properties

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

crc8read-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).

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

idr_idread-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).
rid is the id in reverse order, which is often used in other applications and labeling.

locatorr_locatorread-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 LinkLocator the locatorwillshowaunique8-bytenumber(16characterhexadecimal)startingwithfamilycodeFE.
If no LinkLocator is between the device and the master, the locator field will be all FF.
rlocator is the locator in reverse order.

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

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

Synopsis

Thermometerwithhardwareaddresspins(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 ]]

   DigitalTemperatureSensorwith1KbLockableEEPROM(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-JunctionCompensatedThermocouple(MAX31850andMAX31851)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 ]]

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  temperaturescale that was set for temperature
       measurements.

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

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

   templowread-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

tempresread-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.