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Thermachron(3)

NAME

   DS1921 - Thermochron temperature logging iButton.

SYNOPSIS

   Temperature logging iButton.

   21 [.]XXXXXXXXXXXX[XX][/[
   about/[measuring| resolution| samples| templow| temphigh| version] |
   clock/[date| running| udate] |
   histotgram/[counts[0-62|ALL]| gap| temperature[counts[0-62|ALL]] |
   log[date[0-2047|ALL]|         elements|        temperature[0-2047|ALL]|
   udate[0-2047|ALL]] |
   memory |
   mission/[date| delay| easystart| frequency| rollover| running| samples|
   sampling| udate] |
   overtemp/[date[0-11|ALL]|   elements|  end[0-11|ALL]|  count[0-11|ALL]|
   temperature[0-11|ALL]| udate[0-11|ALL]] |
   pages/page.[0-15|ALL] |
   temperature |
   undertemp/[date[0-11|ALL]|   elements|end[0-11|ALL]|   count[0-11|ALL]|
   temperature[0-11|ALL]| udate[0-11|ALL]] | address | crc8 | id | locator
   | r_address | r_id | r_locator | type ]]

FAMILY CODE

SPECIAL PROPERTIES

   about/measuring
   read-only, yes-no
   Is this DS1921 currently measuring a temperature?

   about/resolution
   read-only, floating point
   What is the resolution of the temperature measurments (in  the  current
   temperature scale).

   about/samples
   read-only, unsigned integer
   How many total temperature measurements has this DS1921 performed?

   about/temphigh
   read-only, floating point
   Highest temperature this DS1921 can measure (in the current temperature
   scale).

   about/templow
   read-only, floating point
   Lowest temperature this DS1921 can measure (in the current  temperature
   scale).

   about/version
   read-only, ascii
   Specific version of this DS1921.

   clock/date
   read-write, ascii
   26  character  date  representation of the internal time stored in this
   DS1921.  Increments once per second while clock/running
   Setting date to a null string will put the current system time.
   Accepted date formats are:
     Sat[urday] March 12 12:23:59 2001
     Apr[il] 4 9:34:56 2002
     3/23/04 23:34:57
     current locale setting (your system's format)

   clock/running
   read-write, yes-no
   Whether the internal clock is running. This can be explicitly set,  and
   is  automatically  started  by  setting clock/date or clock/udate or by
   starting a mission with mission/easystart or mission/frequency

   The main reason to stop the clock is to conserve the internal  battery.
   The  clock  cannot  be  stopped  during  a  mission,  and  the clock is
   essential for a mission.

   clock/udate
   read-write, unsigned integer
   A numeric representation of clock/date
   The number of seconds in UNIX time (since Jan 1, 1970).

   histogram/counts.0 ... histogram/counts.62 histogram/counts.ALL
   read-only, unsigned integer
   The number of samples in the current  mission  whose  temperature  fell
   within the histogram/temperature to histogram/temperature+histogram/gap
   range.

   histogram/elements
   read-only, unsigned integer
   The number of bins in the histogram. Always 63.

   histogram/gap
   read-only, floating point
   The size of the histogram bin. Depends on  the  Thermochron  version  (
   about/version ) and is usually 4 times about/resolution

   Given in the current temperatature scale.

   histogram/temperature.0             ...            histogram/temperature.62
   histogram/temperature.ALL
   read-only, floating point
   Lower limit of the temperature range for  the  corresponding  histogram
   bin. In the current temperature scale.

   log/date.0 ... log/date.2047 log/date.ALL
   read-only, ascii
   Date that the corresponding log/temperature was taken, in ascii format.
   (See clock/date for more on the format).  The number of  valid  entries
   is actually log/elements since the log may not be full.

   mission/samples  gives the total number of samples that have been taken
   but there is only room in the log for 2048 entries.  Once  the  log  is
   full, mission/rollover determines the Thermochron's behavior.

   If  mission/rollover  is  false(0),  the  log  will hold the first 2048
   samples and log/date.0 will always be the same as mission/date

   If mission/rollover is true (1) then the log will hold  the  last  2048
   samples and the entries will be shifted down with each new sample.

   Note  the  OWFS  code  "untwists"  the rollover behavior. The data will
   always be a linear array of earliest to latest.

   ALL is the all data elements comma separated.

   log/elements
   read-only, unsigned integer
   Number of valid entries in the log.  OWFS offers the full  2048  values
   in  the  log memory, but not that many samples may yet have been taken.
   log/elements will range from 0 to 2048 and always be less than or equal
   to mission/samples

   log/temperature.0 ... log/temperature.2047 log/temperature.ALL
   read-write, floating point
   The  temperature  readings  (in  the  current  temperature  scale) that
   correspond to the log/date sample. See  log/date  for  details  on  the
   indexing scheme and rollover behavior.

   log/udate.0 ... log/udate.2047 log/udate.ALL
   read-write, unsigned integer
   A numeric representation of log/date
   The number of seconds in UNIX time (since Jan 1, 1970).

   memory
   read-write, binary
   User  available  storage  space.  512 bytes. Can also be accessed as 16
   pages of 32 bytes with the pages/page.x properties.

   overtemp/count.0 ... overtemp/count.11 overtemp/count.ALL
   undertemp/count.0 ... undertemp/count.11 undertemp/count.ALL
   read-only, unsigned integer
   Number of sampling periods that the Thermochron  stayed  out  of  range
   durring  a  mission.  Each sampling period is mission/frequency minutes
   long.

   overtemp/end.0 ... overtemp/end.11 overtemp/end.ALL
   undertemp/end.0 ... undertemp/end.11 undertemp/end.ALL
   read-only, ascii
   End of time that the Thermochron went out of range during  the  current
   mission. See clock/date for format.

   Each  period  can  be  up  to  255 samples in length, and span the time
   overtemp/date to overtemp/end ( or undertemp/date to undertemp/end ).

   overtemp/date.0 ... overtemp/date.11 overtemp/date.ALL
   undertemp/date.0 ... undertemp/date.11 undertemp/date.ALL
   read-only, ascii
   Time that the Thermochron went out of range during the current mission.
   See clock/date for format.

   overtemp/elements
   undertemp/elements
   read-only, unsigned integer
   Number of entries (0 to 12) in the overtemp or undertemp array.

   overtemp/temperature
   undertemp/temperature
   read-write, floating point
   Temperature limit to trigger alarm and error log.  overtemp/temperature
   gives upper limit and undertemp/temperature gives lower limit.
   In current temperature scale.

   overtemp/udate.0 ... overtemp/udate.11 overtemp/udate.ALL
   undertemp/udate.0 ... undertemp/udate.11 undertemp/udate.ALL
   read-only, unsigned integer
   A numeric representation of overtemp/date or undertemp/date
   The number of seconds in UNIX time (since Jan 1, 1970).

   pages/page.0 ... pages/page.15 pages/page.ALL
   read-write, binary
   Memory is split into 16 pages of 32 bytes each. User available. The log
   memory,  register  banks  and histogram data area are all separate from
   this memory area.
   ALL is an aggregate of the pages. Each page is accessed sequentially.

   temperature
   read-only, floating point
   Last temperature explicitly requested. Only available when the  mission
   is not in progress. Value returned in in the current temperature scale.

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.

ALARMS

   None.

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.

   DS1921 Thermochron
   The  DS1921  (3)  is  an iButton device with many intriguing functions.
   Essentially it monitors temperature, giving both a log of readings, and
   a  histogram  of  temperature  ranges.  The  specification  is somewhat
   complex, but OWFS hides many of the implementation details.

   While on a mission the DS1921 (3) records  temperature  readings  in  a
   2048-sample log and adds them to a 62-bin histogram.

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/DS2438.pdf
   http://pdfserv.maxim-ic.com/en/an/humsensor.pdf

AVAILABILITY

   http://www.owfs.org

AUTHOR

   Paul Alfille (paul.alfille@gmail.com)

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