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DS18B20(3)		     One-Wire File System		    DS18B20(3)

NAME
       DS18B20
	      Programmable Resolution 1-Wire Digital Thermometer

       MAX31820
	      Ambient Temperature Sensor

SYNOPSIS
       Thermometer.

       28  [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9	| tem-
       perature10 | temperature11 | temperature12 die |	 power	|  temphigh  |
       templow	| errata/die | errata/trim | errata/trimblanket	| errata/trim-
       valid | address | crc8 |	id | locator | r_address | r_id	| r_locator  |
       type ]]

FAMILY CODE
       28

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  resolu-
       tion.  There  is	 a tradeoff of time versus accuracy in the temperature
       measurement.

   fasttemp
       read-only, floating point
       Equivalent to temperature9

TEMPERATURE ALARM LIMITS
       When the	device exceeds either temphigh or templow temperature  thresh-
       old  the	device is in the alarm state, and will appear in the alarm di-
       rectory.	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 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 ap-
       plied 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  hexidecimal	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.  Com-
       puted  from the preceding 56 bits of the	unique ID number. Given	as up-
       per case	hexidecimal digits (0-9A-F).

   family
       read-only, ascii
       The 8-bit family	code. Unique to	each type of device.  Given  as	 upper
       case hexidecimal	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 hexidecimal digits (0-9A-F).
       r id is the id in reverse order,	which is often used in other  applica-
       tions 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 hexidecimal)	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 manufac-
       tured  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 (humid-
       ity, 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  en-
       cryption	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, par-
       allel, 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 priciple	is to create a
       virtual filesystem, with	the unique ID being the	directory, and the in-
       dividual	 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 com-
       munication.  Still the fundemental goal has been	ease of	use, flexibil-
       ity 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 pro-
       tean 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 res-
       olution is the best choice unless your application is  truly  time-con-
       strained.

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 hexidecimal,	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

SEE ALSO
   Programs
       owfs (1)	owhttpd	(1) owftpd (1)	owserver  (1)  owdir  (1)  owread  (1)
       owwrite (1) owpresent (1) owtap (1)

   Configuration and testing
       owfs (5)	owtap (1) owmon	(1)

   Language bindings
       owtcl (3) owperl	(3) owcapi (3)

   Clocks
       DS1427  (3)  DS1904(3)  DS1994  (3)  DS2404  (3)	DS2404S	(3) DS2415 (3)
       DS2417 (3)

   ID
       DS2401 (3) DS2411 (3) DS1990A (3)

   Memory
       DS1982 (3) DS1985 (3) DS1986 (3)	 DS1991	 (3)  DS1992  (3)  DS1993  (3)
       DS1995  (3)  DS1996  (3)	 DS2430A  (3) DS2431 (3) DS2433	(3) DS2502 (3)
       DS2506 (3) DS28E04 (3) DS28EC20 (3)

   Switches
       DS2405 (3) DS2406 (3) DS2408 (3)	DS2409 (3) DS2413 (3) DS28EA00 (3)

   Temperature
       DS1822 (3) DS1825 (3) DS1820 (3)	DS18B20	(3)  DS18S20  (3)  DS1920  (3)
       DS1921  (3) DS1821 (3) DS28EA00 (3) DS28E04 (3) EDS0064 (3) EDS0065 (3)
       EDS0066 (3) EDS0067 (3) EDS0068 (3) EDS0071 (3)	EDS0072	 (3)  MAX31826
       (3)

   Humidity
       DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)

   Voltage
       DS2450 (3)

   Resistance
       DS2890 (3)

   Multifunction (current, voltage, temperature)
       DS2436  (3)  DS2437  (3)	 DS2438	 (3)  DS2751 (3) DS2755	(3) DS2756 (3)
       DS2760 (3) DS2770 (3) DS2780 (3)	DS2781 (3) DS2788 (3) DS2784 (3)

   Counter
       DS2423 (3)

   LCD Screen
       LCD (3) DS2408 (3)

   Crypto
       DS1977 (3)

   Pressure
       DS2406 (3) TAI8570 EDS0066 (3) EDS0068 (3)

   Moisture
       EEEF (3)	DS2438 (3)

AVAILABILITY
       http://www.owfs.org

AUTHOR
       Paul Alfille (paul.alfille@gmail.com)

OWFS Manpage			     2003			    DS18B20(3)

NAME | SYNOPSIS | FAMILY CODE | SPECIAL PROPERTIES | TEMPERATURE ALARM LIMITS | TEMPERATURE ERRATA | STANDARD PROPERTIES | DESCRIPTION | ADDRESSING | DATASHEET | SEE ALSO | AVAILABILITY | AUTHOR

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