NAME¶
DS18B20 - Programmable Resolution 1-Wire Digital Thermometer
- MAX31820
- - Ambient Temperature Sensor
SYNOPSIS¶
Thermometer.
28 [.]XXXXXXXXXXXX[XX][/[
fasttemp |
temperature |
temperature9 |
temperature10 |
temperature11 |
temperature12 die |
power |
temphigh |
templow |
errata/die |
errata/trim |
errata/trimblanket |
errata/trimvalid |
address |
crc8 |
id |
locator |
r_address |
r_id |
r_locator |
type ]]
FAMILY CODE¶
28
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.
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 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 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 hexidecimal
digits (0-9A-F).
family¶
read-only, ascii
The 8-bit family code. Unique to each
type of device. Given as upper case
hexidecimal digits (0-9A-F).
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 hexidecimal 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 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?
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 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.
DS18B20¶
The
DS18B20 (3) is one of several available 1-wire temperature sensors.
It is the replacement for the
DS18S20 (3) Alternatives are
DS1822
(3) as well as temperature/voltage measurements in the
DS2436 (3)
and
DS2438 (3). For truly versatile temperature measurements, see the
protean
DS1921 (3) Thermachron (3).
The
MAX31820 is functionally identical to the
DS18B20 except for
it's voltage requirements.
The
DS18B20 (3) can select between 4 resolutions. In general, high
resolution is the best choice unless your application is truly
time-constrained.
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 hexidecimal, 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/DS18B20.pdf
SEE ALSO¶
Programs¶
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)
Clocks¶
DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417
(3)
DS2401 (3) DS2411 (3) DS1990A (3)
Memory¶
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)
Switches¶
DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)
Temperature¶
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) MAX31826 (3)
Humidity¶
DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)
Voltage¶
DS2450 (3)
Resistance¶
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)
Counter¶
DS2423 (3)
LCD Screen¶
LCD (3) DS2408 (3)
Crypto¶
DS1977 (3)
Pressure¶
DS2406 (3) TAI8570 EDS0066 (3) EDS0068 (3)
Moisture¶
EEEF (3) DS2438 (3)
AVAILABILITY¶
http://www.owfs.org
AUTHOR¶
Paul Alfille (paul.alfille@gmail.com)