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DS1821(3)		     One-Wire File System		     DS1821(3)

NAME
       DS1821 -	Programmable Digital Thermostat	and Thermometer

SYNOPSIS
       Thermostat.

       thermostat  [/[	temperature | temphigh | templow | temphighflag	| tem-
       plowflag	| thermostatmode | polarity | 1shot ]]

FAMILY CODE
       none

SPECIAL	PROPERTIES
   temperature
       read-only, floating point
       9-bit resolution	temperature. Units are selected	from the invoking com-
       mand  line.  See	owfs(1)	or owhttpd(1) for choices. Default is Celsius.
       Conversion takes	1 second.

   temphigh templow
       read-write. floating point
       Temperature limits for alarms. Units are	 selected  from	 the  invoking
       command	line.  See  owfs(1) or owhttpd(1) for choices. Default is Cel-
       sius.
       Note that alarms	are not	implemented.

   temphighflag, templowflag
       read-write. yes-no
       temphighflag goes to 1 when temperature exceeds temphigh	and stays at 1
       until  it  is  reset by writing it to zero.  This state persists	across
       power cycles and	operates in both 1-wire	and  thermostat	 modes.	  tem-
       plowflag	 behaves  in the same way, monitoring the temperature with re-
       spect to	templow.

   thermostatmode
       read-write. yes-no
       When this bit is	set to 1 the chip will enter thermostat	 mode  on  the
       next power-up.  See the datasheet for further information on thermostat
       mode.  NOTE: Once the DS1821 has	entered	thermostat mode	it  cannot  be
       taken  out back to 1-wire mode using a 1-wire interface.	 Special elec-
       trical incantations on the power	and data lines must be performed  that
       are  not	possible with a	normal 1-wire bus master. A special circuit is
       required	- see the datasheet for	complete details.

   polarity
       read-write. yes-no
       Controls	the output sense of the	thermostat output (DQ) while in	 ther-
       mostat  mode.   If  polarity is 0 the output is active low. If it is 1,
       active high.

   1shot
       read-write. yes-no
       If this bit is 1, a START CONVERT command will begin a  conversion  and
       the  chip will enter a low power	state when the conversion is complete.
       If the bit is 0 then START CONVERT will begin a	conversion  and	 start
       another	one  as	soon as	it is done.  STOP CONVERSION must be performed
       to get the conversion cycle to stop.  This interface automatically  is-
       sues a STOP CONVERSION command when going out of	continuous mode.

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.

STANDARD PROPERTIES
   type
       read-only, ascii
       Chip type: DS1821

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.

   DS1821
       The DS1821 (3) is a unique 1-wire  device.  It  is  unaddressable,  and
       therefore there can be only one on a given bus.	It is meant to be pro-
       grammed once using 1-wire and then permanently installed	in  a  thermo-
       stat  circuit.	Once  in thermostat mode, it is	no longer programmable
       from a 1-wire interface.	 It is possible	to recover it into 1-wire mode
       but only	with a special circuit.

ADDRESSING
       Unlike all other	1-wire chips, the ,B DS1821 (3)	has no unique address.
       It is addressed as thermostat and will not announce  itself  in	device
       discovery (directory listing).

DATASHEET
       http://pdfserv.maxim-ic.com/en/ds/DS1821.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			     DS1821(3)

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

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