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

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 fundemental 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)