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

# [NAME](#NAME)

**DS1821** - Programmable Digital Thermostat and Thermometer

# [SYNOPSIS](#SYNOPSIS)

Thermostat.

**thermostat** \[/\[ **temperature** | **temphigh** | **templow** | **temphighflag** | **templowflag** | **thermostatmode** | **polarity** | **1shot** ]]

# [FAMILY CODE](#FAMILY_CODE)

*none*

# [SPECIAL PROPERTIES](#SPECIAL_PROPERTIES)

## [temperature](#temperature)

*read-only, floating point*  
9-bit resolution temperature. Units are selected from the invoking command line. See [**owfs(1)**](/man/os/owfs/owfs.1) or [**owhttpd(1)**](/man/os/owfs/owhttpd.1) for choices. Default is Celsius. Conversion takes 1 second.

## [temphigh templow](#temphigh_templow)

*read-write. floating point*  
Temperature limits for alarms. Units are selected from the invoking command line. See [**owfs(1)**](/man/os/owfs/owfs.1) or [**owhttpd(1)**](/man/os/owfs/owhttpd.1) for choices. Default is Celsius.  
Note that alarms are not implemented.

## [temphighflag, templowflag](#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. **templowflag** behaves in the same way, monitoring the temperature with respect to **templow.**

## [thermostatmode](#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 electrical 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](#polarity)

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

## [1shot](#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 issues a STOP CONVERSION command when going out of continuous mode.

See the file man3/temperature\_threshold.3so.

# [STANDARD PROPERTIES](#STANDARD_PROPERTIES)

## [type](#type)

*read-only, ascii*  
Chip type: DS1821

# [DESCRIPTION](#DESCRIPTION)

See the file man3/description.3so.

## [DS1821](#DS1821)

The [**DS1821 (3)**](/man/os/owfs/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 programmed once using 1-wire and then permanently installed in a thermostat 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](#ADDRESSING)

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

# [DATASHEET](#DATASHEET)

http://pdfserv.maxim-ic.com/en/ds/DS1821.pdf

# [SEE ALSO](#SEE_ALSO)

See the file man3/seealso.3so.

# [AVAILABILITY](#AVAILABILITY)

http://www.owfs.org

# [AUTHOR](#AUTHOR)

Paul Alfille (paul.alfille@gmail.com)

2003 OWFS Manpage

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Document: DS1821(3) from owfs 3.2.4-r8 (Chainguard OS)
Source: https://github.com/owfs/owfs