DS1821(3) One-Wire File System DS1821(3)NAMEDS1821 - 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
respect 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
issues a STOP CONVERSION command when going out of continuous mode.
STANDARD PROPERTIES
type
read-only, ascii
Chip type: DS1821DESCRIPTIONDS1821
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 ALSOAVAILABILITY
http://www.owfs.org
AUTHOR
Paul Alfille (paul.alfille@gmail.com)
OWFS Manpage 2003 DS1821(3)
