Ubuntu Manpage: DS18S20

NAME

       DS18S20
              - High-Precision 1-Wire Digital Thermometer

       DS1920 - iButton version of the thermometer

SYNOPSIS

       Thermometer.

       10  [.]XXXXXXXXXXXX[XX][/[  fasttemp  |  temperature  |  temperature9  |  temperature10 | temperature11 |
       temperature12 | latesttemp | die | power | temphigh | templow | trim | trimblanket | trimvalid |  address
       | crc8 | id | locator | r_address | r_id | r_locator | type ]]

FAMILY CODE

SPECIAL PROPERTIES

   power
       read-only,yes-no
       Is the chip powered externally (=1) or from the parasitically from the data bus (=0)?

   temperature
       read-only, floating point
       Measured temperature with 12 bit resolution.

   temperature9 temperature10 temperature11 temperature12
       read-only, floating point
       Measured  temperature  at  9  to  12  bit  resolution. There is a tradeoff of time versus accuracy in the
       temperature measurement.

   latesttemp
       read-only, floating point
       Measured temperature at 9 to 12 bit resolution, depending on the resolution of the latest  conversion  on
       this chip. Reading this node will never trigger a temperature conversion. Intended for use in conjunction
       with /simultaneous/temperature.

   fasttemp
       read-only, floating point
       Equivalent to temperature9

TEMPERATURE ALARM LIMITS

       When the device exceeds either temphigh or templow temperature threshold  the  device  is  in  the  alarm
       state,  and  will  appear in the alarm directory. 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.

TEMPERATURE ERRATA

       There are a group of obscure internal properties exposed to protect against an hardware defect in certain
       batches  of  the  B7  die  of  some  DS18x20  chips. See http://www.1wire.org/en-us/pg_18.html or request
       AN247.pdf from Dallas directly.

   errata/die
       read-only,ascii
       Two character manufacturing die lot. "B6" "B7" or "C2"

   errata/trim
       read-write,unsigned integer
       32 bit trim value in the EEPROM of the chip. When written, it does not seem to  read  back.  Used  for  a
       production problem in the B7 die.

       Read allowed for all chips. Only the B7 chips can be written.

   errata/trimblanket
       read-write,yes-no
       Writing non-zero (=1) puts a default trim value in the chip. Only applied to the B7 die.  Reading will be
       true (non-zero) if trim value is the blanket value. Again, only B7 chips will register  true,  and  since
       the written trim values cannot be read, this value may have little utility.

   errata/trimvalid
       read-only,yes-no
       Is the trim value in the valid range? Non-zero if true, which includes all non-B7 chips.

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.

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.

DS18S20 DS1920
The DS18S20 (3) is one of several available 1-wire temperature sensors. It has been largely replaced by
the DS18B20 (3) and DS1822 (3) as well as temperature/vlotage measurements in the DS2436 (3) and DS2438
(3). For truly versatile temperature measurements, see the protean DS1921 (3) Thermachron (3).

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/DS18S20.pdf

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)