DS18B20(3) One-Wire File System DS18B20(3) NAME DS18B20 - Programmable Resolution 1-Wire Digital Thermometer MAX31820 - Ambient Temperature Sensor SYNOPSIS Thermometer. 28 [.]XXXXXXXXXXXX[XX][/[ fasttemp | temperature | temperature9 | tempera- ture10 | temperature11 | temperature12 | latesttemp | die | power | tem- phigh | templow | tempres | errata/die | errata/trim | errata/trimblanket | errata/trimvalid | address | crc8 | id | locator | r_address | r_id | r_lo- cator | 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. 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 /simultane- ous/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, espe- cially 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 RESOLUTION DEFAULT VALUE tempres read-write, integer The device employs a non-volatile memory to store the default temperature resolution (9, 10, 11 or 12 bits) to be applied after power-up. This is useful if you use simultaneous temperature conversions. Reading this node gives you the value stored in the non-volatile memory. Writing sets a new power-on resolution value. As a side effect, reading this node resets the temperature resolution used by simultaneous temperature conversions to its power-on value. It also af- fects the resolution value used by latesttemp, to scale the latest conver- sion value, so make sure to re-sample the temperature before accessing lat- esttemp after writing or reading the tempres value. 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 blan- ket 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 ap- plications 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 asso- ciated 1-wire physical connections with a unique 1-wire code. If the con- nection is behind a Link Locator the locator will show a unique 8-byte num- ber (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-connec- tor 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, temper- ature, 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 indi- vidually 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 con- sistent interface. The goal is to provide an easy set of tools for a soft- ware 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 fundamental goal has been ease of use, flexibility and correct- ness 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) Ther- machron (3). The MAX31820 is functionally identical to the DS18B20 except for it's volt- age requirements. The DS18B20 (3) can select between 4 resolutions. In general, high resolu- tion 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 ad- dress 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/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) ID 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) Infer- noEmbedded (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 (3) EDS0066 (3) EDS0068 (3) Moisture EEEF (3) DS2438 (3) AVAILABILITY http://www.owfs.org AUTHOR Paul Alfille (paul.alfille@gmail.com) OWFS Manpage 2003 DS18B20(3)
NAME | SYNOPSIS | FAMILY CODE | SPECIAL PROPERTIES | TEMPERATURE ALARM LIMITS | TEMPERATURE RESOLUTION DEFAULT VALUE | TEMPERATURE ERRATA | STANDARD PROPERTIES | DESCRIPTION | ADDRESSING | DATASHEET | SEE ALSO | AVAILABILITY | AUTHOR
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