Ubuntu Manpage: DS18B20

NAME

       DS18B20
              - Programmable Resolution 1-Wire Digital Thermometer

       MAX31820
              - Ambient Temperature Sensor

SYNOPSIS

       Thermometer.

       28  [.]XXXXXXXXXXXX[XX][/[  fasttemp  |  temperature  |  temperature9  |  temperature10  |
       temperature11 | temperature12 | latesttemp | die | power | temphigh | templow | tempres  |
       errata/die  |  errata/trim | errata/trimblanket | errata/trimvalid | address | crc8 | id |
       locator | r_address | r_id | r_locator | type ]]

FAMILY CODE

SPECIAL PROPERTIES

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

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

   temperature9 temperature10 temperature11 temperature12
       read-only, floating point
       Measured temperature at 9 to 12 bit  resolution.  There  is  a  tradeoff  of  time  versus
       accuracy in the temperature measurement.

   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

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.

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.

TEMPERATURE ERRATA

       There are a group of obscure internal properties exposed to protect  against  an  hardware
       defect   in   certain   batches   of   the   B7   die   of   some   DS18x20   chips.   See
       http://www.1wire.org/en-us/pg_18.html or request AN247.pdf from Dallas directly.

   errata/die
       read-only,ascii
       Two character manufacturing die lot. "B6" "B7" or "C2"

   errata/trim
       read-write,unsigned integer
       32 bit trim value in the EEPROM of the chip. When written, it does not seem to read  back.
       Used for a production problem in the B7 die.

       Read allowed for all chips. Only the B7 chips can be written.

   errata/trimblanket
       read-write,yes-no
       Writing  non-zero  (=1) puts a default trim value in the chip. Only applied to the B7 die.
       Reading will be true (non-zero) if trim value is the blanket value. Again, only  B7  chips
       will  register true, and since the written trim values cannot be read, this value may have
       little utility.

   errata/trimvalid
       read-only,yes-no
       Is the trim value in the valid range? Non-zero if true, which includes all non-B7 chips.

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.

DS18B20
The DS18B20 (3) is one of several available 1-wire temperature sensors. It is the
replacement for the DS18S20 (3) Alternatives are 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 MAX31820 is functionally identical to the DS18B20 except for it's voltage
requirements.
The DS18B20 (3) can select between 4 resolutions. In general, high resolution is the best
choice unless your application is truly time-constrained.

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/DS18B20.pdf

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)