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       DS1921 - Thermachron temperature logging iButton.


       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 ]]




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

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

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

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

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

       read-only, ascii
       Specific version of this DS1921.

       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)

       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.

       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.

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

       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.

       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).

       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

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

       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.

       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.


       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

       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 hexidecimal  digits  (0-9A-

       read-only, ascii
       The  8-bit  family  code.  Unique  to each type of device. Given as upper case hexidecimal
       digits (0-9A-F).

       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 applications and labeling.

       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?

       read-only, ascii
       Part name assigned by Dallas Semi. E.g.  DS2401 Alternative packaging  (iButton  vs  chip)
       will not be distiguished.




       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 priciple 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

       While  on  a  mission the DS1921 (3) records temperature readings in a 2048-sample log and
       adds the to 62-bin histogram. more complete form of the DS2438 (3) battery  chip.  Current
       sensing  is available, but not implemented. The major advantage compared to the DS2436 (3)
       is that two voltages can be read, allowing  correcting  circuit  nmeasurements  to  supply
       voltage and temperature.


       All  1-wire  devices  are factory assigned a unique 64-bit address. This address is of the

       Family Code
              8 bits

              48 bits

       CRC    8 bits

       Addressing under OWFS is in hexidecimal, of form:


       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.



       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)

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

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

       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)

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

       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)

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

       DS2450 (3)

       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)

       DS2423 (3)

   LCD Screen
       LCD (3) DS2408 (3)

       DS1977 (3)

       DS2406 (3) -- TAI8570 EDS0066 (3) EDS0068 (3)



       Paul Alfille (